Can no longer boot into Mavericks 10.9.5

Question

My problem is that I can no longer boot into Mavericks 10.9.5 on my mid-2012 Macbook Pro.  The problem arose suddenly without any known major changes to my software or hardware.  The booting process freezes with the apple visible and the circle below it spinning endlessly.  Every several seconds, the display very briefly gets brighter, then the circle starts spinning again and the process repeats itself.  It never gets to the user login screen.
Other than keeping various apps up to date, I don't recall any recent major operating system or other major software updates, nor have I made any recent hardware changes.  I've searched a multitude of threads and and tried any number of fixes without success.  Here's what I've tried so far (and probably a few more that I can't remember): (1) Repaired the startup disk with both Recovery HD -> Disk Utility and single-user mode -> /sbin/fsck -fy; (2) Repaired the startup disk permissions with Recovery HD -> Disk Utility; (3) Reloaded the Mavericks 10.9.5 operating system twice; (4) deleted /Library/Preferences/com.apple.loginwindow.plist; (5) reset PRAM and NVRAM; (6) booted with "D" pressed and ran the Apple hardware test, which ran for about 40 minutes and reported no problems; (7) tried booting from a bootable clone of Mavericks 10.9.5 on an external hard drive, which also failed at the same place with the apple showing and the circle below it spinning endlessly.  ***Oddly, I am able to boot from a bootable clone of Mountain Lion on an external hard drive.  It's Mavericks that won't boot.***
Here is the part of the system log the repeats itself over and over and seems to correlate with the repeated failed attempts to complete the booting process.  Any help would be appreciated beyond words:
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Server is starting up
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Session 256 retained (2 references)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Session 256 released (1 references)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Session 256 retained (2 references)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: init_page_flip: page flip mode is on
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 54 modes for display 0x00000000 [54, 0]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 1 modes for display 0x00000000 [1, 0]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 51 modes for display 0x00000000 [51, 0]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 1 modes for display 0x00000000 [1, 0]
May  2 12:49:01 --- last message repeated 1 time ---
May  2 12:49:01 SCH-MacBookPro kernel[0]: IOHIDSystem::registerScreenGated: Screen 0 recycled from pid 343
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: mux_initialize: Mode is dynamic
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 54 modes for display 0x00000000 [54, 0]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 1 modes for display 0x00000000 [1, 0]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 51 modes for display 0x00000000 [51, 0]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Found 1 modes for display 0x00000000 [1, 0]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: WSMachineUsesNewStyleMirroring: true
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: MPServiceForDisplayDevice: Invalid device alias (0)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x04248378: GL mask 0x10; bounds (0, 0)[2560 x 1440], 51 modes available
  Main, Active, on-line, enabled, Vendor 610, Model 9227, S/N 162f0ab5, Unit 4, Rotation 0
  UUID 0x3ef17c2fc9ab601507ec022fbd95576c
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x003f003d: GL mask 0x2; bounds (0, 0)[4096 x 2160], 2 modes available
  off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 1, Rotation 0
  UUID 0xffffffffffffffffffffffffffffffff
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x003f0041: GL mask 0x20; bounds (0, 0)[0 x 0], 1 modes available
  off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 5, Rotation 0
  UUID 0xffffffffffffffffffffffffffffffff
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x003f003f: GL mask 0x8; bounds (0, 0)[0 x 0], 1 modes available
  off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 3, Rotation 0
  UUID 0xffffffffffffffffffffffffffffffff
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x04280142: GL mask 0x5; bounds (2560, 0)[1680 x 1050], 54 modes available
  Active, on-line, enabled, built-in, boot, Vendor 610, Model a005, S/N 0, Unit 2, Rotation 0
  UUID 0xde23f9c1cf7b915b2afe83aecee77b54
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: WSSetWindowTransform: Singular matrix
May  2 12:49:01 --- last message repeated 1 time ---
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x04248378: GL mask 0x10; bounds (0, 0)[2560 x 1440], 51 modes available
  Main, Active, on-line, enabled, Vendor 610, Model 9227, S/N 162f0ab5, Unit 4, Rotation 0
  UUID 0x3ef17c2fc9ab601507ec022fbd95576c
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x003f003d: GL mask 0x2; bounds (3584, 0)[1 x 1], 2 modes available
  off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 1, Rotation 0
  UUID 0xffffffffffffffffffffffffffffffff
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x003f0041: GL mask 0x20; bounds (3585, 0)[1 x 1], 1 modes available
  off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 5, Rotation 0
  UUID 0xffffffffffffffffffffffffffffffff
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x003f003f: GL mask 0x8; bounds (3586, 0)[1 x 1], 1 modes available
  off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 3, Rotation 0
  UUID 0xffffffffffffffffffffffffffffffff
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x04280142: GL mask 0x5; bounds (435, -1050)[1680 x 1050], 54 modes available
  Active, on-line, enabled, built-in, boot, Vendor 610, Model a005, S/N 0, Unit 2, Rotation 0
  UUID 0xde23f9c1cf7b915b2afe83aecee77b54
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: CGXPerformInitialDisplayConfiguration
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]:   Display 0x04248378: Unit 4; Vendor 0x610 Model 0x9227 S/N 372181685 Dimensions 23.50 x 13.23; online enabled, Bounds (0,0)[2560 x 1440], Rotation 0, Resolution 1
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]:   Display 0x003f003d: Unit 1; Vendor 0xffffffff Model 0xffffffff S/N -1 Dimensions 0.00 x 0.00; offline enabled, Bounds (3584,0)[1 x 1], Rotation 0, Resolution 1
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]:   Display 0x003f0041: Unit 5; Vendor 0xffffffff Model 0xffffffff S/N -1 Dimensions 0.00 x 0.00; offline enabled, Bounds (3585,0)[1 x 1], Rotation 0, Resolution 1
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]:   Display 0x003f003f: Unit 3; Vendor 0xffffffff Model 0xffffffff S/N -1 Dimensions 0.00 x 0.00; offline enabled, Bounds (3586,0)[1 x 1], Rotation 0, Resolution 1
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]:   Display 0x04280142: Unit 2; Alias(2, 0x5); Vendor 0x610 Model 0xa005 S/N 0 Dimensions 13.03 x 8.15; online enabled built-in, Bounds (435,-1050)[1680 x 1050], Rotation 0, Resolution 1
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: CGXMuxBoot: Boot normal
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: GLCompositor: GL renderer id 0x01024400, GL mask 0x00000003, accelerator 0x00004f2f, unit 0, caps QEX|MIPMAP, vram 1024 MB
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: GLCompositor: GL renderer id 0x01024400, GL mask 0x00000003, texture max 16384, viewport max {16384, 16384}, extensions FPRG|NPOT|GLSL|FLOAT
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: GLCompositor: GL renderer id 0x01022727, GL mask 0x0000003c, accelerator 0x00004907, unit 2, caps QEX|MIPMAP, vram 1024 MB
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: GLCompositor: GL renderer id 0x01022727, GL mask 0x0000003c, texture max 16384, viewport max {16384, 16384}, extensions FPRG|NPOT|GLSL|FLOAT
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: GLCompositor enabled for tile size [256 x 256]
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: CGXGLInitMipMap: mip map mode is on
May  2 12:49:01 SCH-MacBookPro.local loginwindow[353]: **DMPROXY** Found `/System/Library/CoreServices/DMProxy'.
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x04248378: Unit 4; ColorProfile { 2, "Thunderbolt Display"}; TransferFormula (1.000000, 1.000000, 1.000000)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Display 0x04280142: Unit 2; ColorProfile { 3, "Color LCD"}; TransferTable (256, 12)
May  2 12:49:01 SCH-MacBookPro.local launchctl[356]: launchctl: Dubious permissions on file (skipping): /Library/LaunchAgents/com.adobe.AAM.Updater-1.0.plist
May  2 12:49:01 SCH-MacBookPro.local launchctl[356]: com.apple.findmymacmessenger: Already loaded
May  2 12:49:01 SCH-MacBookPro.local com.apple.SecurityServer[23]: Session 100021 created
May  2 12:49:01 SCH-MacBookPro.local UserEventAgent[357]: Failed to copy info dictionary for bundle /System/Library/UserEventPlugins/alfUIplugin.plugin
May  2 12:49:01 SCH-MacBookPro.local airportd[71]: _doAutoJoin: Already associated to “schuyler”. Bailing on auto-join.
May  2 12:49:01 SCH-MacBookPro.local loginwindow[353]: Setting the initial value of the magsave brightness level 1
May  2 12:49:01 SCH-MacBookPro.local loginwindow[353]: Login Window Started Security Agent
May  2 12:49:01 SCH-MacBookPro.local ManagedClient[362]: ApplePersistence=YES
May  2 12:49:01 SCH-MacBookPro.local SecurityAgent[363]: Failed to create agent mechanism, failing authentication!
May  2 12:49:01 SCH-MacBookPro.local com.apple.authd[84]: engine[353]: error creating mechanism agent
May  2 12:49:01 SCH-MacBookPro.local com.apple.authd[84]: engine[353]: evaluate returned -60008 returning errAuthorizationInternal
May  2 12:49:01 SCH-MacBookPro.local loginwindow[353]: Login Window - Returned from Security Agent
May  2 12:49:01 SCH-MacBookPro.local loginwindow[353]: ERROR | -[LoginApp performAuthPluginRequest:] | AuthorizationRef doesn't have a username. Exiting.
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: CGXRestartSessionWorkspace: session workspace exited for session 256 (on console)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Session 256 released (1 references)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: Session 256 released (0 references)
May  2 12:49:01 SCH-MacBookPro.local WindowServer[354]: loginwindow connection closed; closing server.
May  2 12:49:03 SCH-MacBookPro com.apple.launchd[1] (com.apple.loginwindow): Throttling respawn: Will start in 1 seconds
May  2 12:49:04 SCH-MacBookPro.local loginwindow[364]: Login Window Application Started
May  2 12:49:04 SCH-MacBookPro com.apple.launchd[1] (com.apple.WindowServer): Throttling respawn: Will start in 7 seconds

Answer 1

Hi
You got a prob I think, if you can boot a windows, MSconfig, startup options might restore the boot files.Only other thing is to try and either load a new windows and let it setup a boot file, or perhaps a win98 startup disk, and fdisk, then set active partiton, which will set an MBR.  But that would leave a load of work to do, I think I'd opt for an install of XP, and let it repair existing installation, and make a new boot file.
Hope you don't need the info on disks.  If you do, I would install another HDD, load XP, then copy original Disk to save place.
Good luck
Jocko