Windows partition will not open using Boot Camp on iMac 10.9.5

Question

OS:  27" desktop iMac, Maverick 10.9.5, 8 GB RAM
HD Partions:  iMac OS X, Windows 7,  Boot Camp
For some unknown reason I am having problems getting Windows 7 to open after starting up in Boot Camp, and it's getting progressively worse. After starting Boot Camp I select the Windows 7 partition and either click on that icon or press "Return/Enter". This is where everything freezes and I have to shut down and reboot again into Boot Camp to try again. Sometimes it works, other times not. I've already tried 8 times tonight but can't get into the Windows 7 partition. The OS X partition and everything else is working fine and I have all of my updates.
Any help or suggestions is greatly appreciated.
Thanks,
Dennis

Answer 1

I am trying to boot into an existing W7. When I turned on the computer this morning I booted straight into Boot Camp and then successfully went into W7 with no problems, never going into the OS X partition. I later rebooted straight into OS X (the default startup) and read your comments.
I entered the four lines of commands you suggested in Terminal and this is what I got...
dennisetonsimac:~ denedg$
dennisetonsimac:~ denedg$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            837.0 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   4:       Microsoft Basic Data BOOTCAMP                162.3 GB   disk0s4
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *500.1 GB   disk1
   1:               Windows_NTFS FreeAgent GoFlex Drive  500.1 GB   disk1s1
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Time Machine Backups    499.8 GB   disk2s2
dennisetonsimac:~ denedg$
dennisetonsimac:~ denedg$ diskutil cs list
No CoreStorage logical volume groups found
dennisetonsimac:~ denedg$ sudo gpt -vv -r show /dev/disk0
WARNING: Improper use of the sudo command could lead to data loss
or the deletion of important system files. Please double-check your
typing when using sudo. Type "man sudo" for more information.
To proceed, enter your password, or type Ctrl-C to abort.
Password:
Sorry, try again.
Password:
gpt show: /dev/disk0: mediasize=1000204886016; sectorsize=512; blocks=1953525168
gpt show: /dev/disk0: Suspicious MBR at sector 0
gpt show: /dev/disk0: Pri GPT at sector 1
gpt show: /dev/disk0: Sec GPT at sector 1953525167
       start        size  index  contents
           0           1         MBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6        
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640  1634773168      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  1635182808     1269544      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  1636452352   317071360      4  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  1953523712        1423        
  1953525135          32         Sec GPT table
  1953525167           1         Sec GPT header
dennisetonsimac:~ denedg$ sudo fdisk /dev/disk0
Password:
Sorry, try again.
Password:
Disk: /dev/disk0 geometry: 121601/255/63 [1953525168 sectors]
Signature: 0xAA55
         Starting       Ending
#: id  cyl  hd sec -  cyl  hd sec [     start -       size]
1: EE 1023 254  63 - 1023 254  63 [         1 -     409639] <Unknown ID>
2: AF 1023 254  63 - 1023 254  63 [    409640 - 1634773168] HFS+       
3: AB 1023 254  63 - 1023 254  63 [1635182808 -    1269544] Darwin Boot
*4: 07 1023 254  63 - 1023 254  63 [1636452352 -  317071360] HPFS/QNX/AUX
dennisetonsimac:~ denedg$