Also check your Event Viewer for any critical errors or warnings in the logs. If nothing in your event viewer run these two tests.
1)
Memtest86:
http://www.memtest86.com
In order to check your RAM you're going need to do a test, download and burn the iso onto a disk, and boot the CD
Follow the on-screen instructions.
Now let the test run for at least 6 passes. Every time the program returns an error that means your RAM is corrupted, bad, or faulted, or the motherboard is bad, or faulted and/or corrupted. If you get an error then you should try by booting up your computer with each RAM inserted separately one at a time. When you find one that doesn't return any errors then test it in every single RAM socket to test for a bad slot.
If you can't find any errors with that, then next thing to test would be with driver verifier
You should do a backup of your data first. Make a System Restore point. You should also have a startup repair disk, this will help you with a lot of problems that your computer has
In Windows 7 you can make a Startup Repair disk by going to Start > All Programs > Maintenance > Create a System Repair Disc and with Windows Vista you'll have to use your installation disk or the "Repair your computer" option at the top of the Safe Mode menu .
2)
Driver Verifier:
- Go to Start and type in "Verifier" (without quotes) and press Enter when "Driver Verifier" is selected
- Choose "Create custom settings (for code developers)" and click next
- Choose "Select individual settings from a full list" and click next
- Choose everything
except for "Low Resource Simulation" and click next
- Choose "Select driver names from a list" and click next, then select all drivers
not provided by Microsoft and click next
- Click "Finish".
Reboot the system and wait for it to crash to the Blue Screen. Continue to use your system normally, and if you know what causes the crash (Opening Windows Media Center), do that repeatedly. The objective here is to get the system to crash because Driver Verifier is making the drivers work. If it doesn't crash for you, then let your system run for at least 48 hours.
If you can't get into Windows because it crashes immediately, try booting in Safe Mode. And if you can't get into Safe Mode, try doing a System Restore to set the system back to the previous restore point that you created.
Make sure you have minidumps enabled, and post the minidump so I can review it.