Intermittent BSOD

Unfortunately, the BSOD's don't reveal a whole bunch. They seem to hint at a hardware problem, so please start with these free diagnostics:

CHKDSK /R /F:
Run CHKDSK /R /F from an elevated (Run as adminstrator) Command Prompt. Please do this for each hard drive on your system.
When it tells you it can't do it right now - and asks you if you'd like to do it at the next reboot - answer Y (for Yes) and press Enter. Then reboot and let the test run. It may take a while for it to run, but keep an occasional eye on it to see if it generates any errors. See "CHKDSK LogFile" below in order to check the results of the test.

Elevated Command Prompt:
Go to Start and type in "cmd.exe" (without the quotes)
At the top of the Search Box, right click on Cmd.exe and select "Run as administrator"

CHKDSK LogFile:
Go to Start and type in "eventvwr.msc" (without the quotes) and press Enter
Expand the Windows logs heading, then select the Application log file entry.
Double click on the Source column header.
Scroll down the list until you find the Chkdsk entry (wininit for Win7) (winlogon for XP).
Copy/paste the results into your next post.

Please start by running these bootable hardware diagnostics:
Memory Diagnostics (read the details at the link)
HD Diagnostic (read the details at the link)

Also, please run one of these free, independent online malware scans to ensure that your current protection hasn't been compromised: Malware (read the details at the link)

Then, if the above tests pass, I'd try these free stress tests:

FurMark download site: FurMark: VGA Stress Test, Graphics Card and GPU Stability Test, OpenGL Benchmark and GPU Temperature | oZone3D.Net
FurMark Setup:
- If you have more than one GPU, select Multi-GPU during setup
- In the Run mode box, select "Stability Test" and "Log GPU Temperature"
Click "Go" to start the test
- Run the test until the GPU temperature maxes out - or until you start having problems (whichever comes first).
- Click "Quit" to exit

Prime95 download site: Free Software - GIMPS
Prime95 Setup:
- extract the contents of the zip file to a location of your choice
- double click on the executable file
- select "Just stress testing"
- select the "Blend" test. If you've already run MemTest overnight you may want to run the "Small FFTs" test instead. (run all 3 if you find a problem and note how long it takes to error out with each)
- "Number of torture test threads to run" should equal the number of CPU's times 2 (if you're using hyperthreading).
The easiest way to figure this out is to go to Task Manager...Performance tab - and see the number of boxes under CPU Usage History
Then run the test for 6 to 24 hours - or until you get errors (whichever comes first).
This won't necessarily crash the system - but check the output in the test window for errors.
The Test selection box and the stress.txt file describes what components that the program stresses.

Two other video stress tests (may be more stressful than FurMark):
Video Memory stress Test - МИРNVIDIA / Утилиты / VMT
Artifact Locator - МИРNVIDIA / Утилиты / Artifact Locator
Sorry, but I don't read the language that this website is made in.

If that doesn't nail down the problem, please post back and we'll see what else we can try.

BSOD BUGCHECK SUMMARY

Code:

Built by: 7600.16617.x86fre.win7_gdr.100618-1621
Debug session time: Thu Sep  2 20:06:17.304 2010 (UTC - 4:00)
System Uptime: 0 days 0:07:57.662
BUGCHECK_STR:  0x50
PROCESS_NAME:  System
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨``
Built by: 7600.16617.x86fre.win7_gdr.100618-1621
Debug session time: Thu Sep  2 19:55:10.920 2010 (UTC - 4:00)
System Uptime: 0 days 9:00:19.278
PROCESS_NAME:  System
BUGCHECK_STR:  0x24
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨``