Wi-Fi turns itself off and will not turn back on

Question

Right, I had to create a new Apple ID just to access the forum, because for some reason the ID I've had since they existed just throws up a "Page Not Found" error when I log in (backsoon/error URL).  That was just the most sour and rotten cherry on this cake...
So, I have a Mid-2012 MacBook Pro, updated to 10.9.5.  For a very long time my bluetooth has been unavailable.  The menubar icon is grey and has the broken bolt through it, the presence pane is missing, and under System Information it finds no hardware.  This was annoying but not particularly problematic, as I rarely if ever use bluetooth.  I only mention this because I know the BT & Wi-Fi board is the same item.
Of late, however, something much more troubling has started occurring.  My Wi-Fi has been giving me the most obnoxious problem I have ever had with a computer.  At a seemingly random interval that has rapidly shortened to at most 30 minutes, sometimes as low as a single minute, the Wi-Fi will turn off without me knowing.  What I mean is, while the menubar icon will still show full strength, all internet apps lose connection.  If I click the icon, the pulldown menu is devoid of all networks (including the one it is supposedly connected to), and does not find any networks after searching.  If I turn the Wi-Fi off (as though to cycle it off-on), it will not turn back on.  If instead of looking at the menubar pulldown, I go into System Preferences, Wi-Fi is listed as "Off" already and it likewise cannot be turned on.
System Information does still show the actual hardware card as existing, unlike the BT card.
The only two changes since this started occurring (though the BT was gone then as well) were switching from a B/G router to an N router, and the October 25th 2014-005 Security Update.  And yes, all our other devices (windows laptop, Yosemite MBP Retina, iPad 1, iPhone 4, 5 & 5S, HP Photosmart which I cannot print to with no wifi) all connect to the Wi-Fi fine.
So far, I have tried:
• Removing all the network-associated .plist files.
• Resetting the PRAM & SMC.
• Creating a new location in System Prefs with only Wi-Fi in it.
• Making Wi-Fi inactive and re-activating it in System Prefs.
• Verified/Repaired Permissions
• I believe I have verified the drive, but I will try again.
I have not yet tried reinstalling the system, or a clean install.  The reason for this is the same reason I cannot bring the computer to a genius bar (yes, AppleCare is still active).  I cannot be without this computer, I am an engineering student with finals less than a three weeks away, I have projects and homeworks due even across the coming Thanksgiving break.  Luckily it waited until this weekend to become truly infuriating, so I may have a chance to try a reinstall and/or clean install.
Any suggestions further would be greatly appreciated.  I'm not one to buy into conspiracy theories, but...  This basically started happening a week after Yosemite came out (which I cannot yet upgrade to because its Java version breaks MatLab, and the workaround is too kludgy for me to use).

Answer 1

This is just like my problem on my 2011 MacBookPro. It drops the wifi connection repeatedly. Sometimes it will reconnect immediately when prompted , sometimes it takes 10 or 20 attempts to login with the router password, continually reporting "incorrect password' until it suddenly connects with that same password!  Sometimes it will then drop that connection within half a minute , sometimes longer. I kept thinking it was a BT internet problem but my iMac, iPad and iPhone all remain connected to the same wifi with no problems. The iMac is also running Yosemite 10.10.1 .  I understand this is a known problem. When will Apple release a fix??