I have a fairly new installation of Windows 7 which now goes to blue screen on every login attempt. At first, I thought it might be from memory incompatibility because I just installed new chips, but the same machine boots Ubuntu 12.04 just fine and shows the correct amount of RAM. I ran memtest anyway and it returned no errors after about 2 1/2 hours.
I've also run
chkdsk /f c:
(not from Recover Console, but scheduled on boot from Safe Mode) on startup. chkdsk said it found and fixed errors, but I still get a blue screen.
I'm starting to suspect the hardware problems, but I want to eliminate other, fixable possibilities before springing for a new HDD.
Can someone who knows point me in the right direction?
The Stop 0x50 message indicates that requested data was not in memory. The system generates an exception error when using a reference to an invalid system memory address. Defective memory (including main memory, L2 RAM cache, video RAM) or incompatible software (including remote control and antivirus software) might cause Stop 0x50 messages.
Possible Resolutions:
• If you added new hardware recently, remove and replace the hardware to determine if it is causing or contributing to the problem. Run diagnostics software supplied by the hardware manufacturer to determine if the component has failed.
• Stop 0x50 messages can also occur after installing faulty drivers or system services. If the file name is listed, you need to disable, remove, or roll back that driver. If not, disable the recently installed service or application to determine if this resolves the error. If this does not resolve the problem, contact the hardware manufacturer for updates. Using updated drivers and software is especially important for network interface cards, video adapters, backup programs, multimedia applications, antivirus scanners, and CD mastering tools. If an updated driver is not available, attempt to use a driver from a similar device in the same family. For example, if printing to a Model 1100C printer causes Stop 0x50 errors, using a printer driver meant for a Model 1100A or Model 1000 might temporarily resolve the problem.
If you have not changed any drivers or hardware recently, I would suspect faulty or an incorrectly seated RAM module.
Check that your RAM is correctly seated and if so, run a Memtest86 to see if any RAM faults are picked up. Even one fault will indelicate bad RAM.
Just following up in hopes that this may help other users in the future.
Switching the new memory chips out for the old ones didn't solve the problem, it just resulted in a blue screen with different error messages. So I replaced the new memory chips and booted the Windows 7 install, chose "repair" and got myself a command prompt.
I did:
chkdsk /f c:
from the cd and it found and fixed filesystem errors.
Once again, scheduling Windows to perform this operation on next boot from inside Safe Mode didn't work. I had to do it from the installation disk, presumably so chkdsk could operate on the filesystem while it wasn't mounted.
Everything appears fine now and I can use the system with the new memory. I'll know that if the problem reoccurs I should suspect hdd failure - this machine is from 2007 and has never had a new disk.
Letting us all know how you resolved the problem helps everybody, including this boy 
Thank you,
Lee