Once in a while I'd be browsing the web, on MS Word or have left my PC on for an overnight download, and I'd get a totally unexpected BSOD. 4 months and 24 BSODs later I'm still perplexed as to what's wrong.
Hitting up BlueScreenView it looks like,
- Most common error: IRQL_NOT_LESS_OR_EQUAL (18 times)
- Followed by KERNEL_MODE_EXCEPTION_NOT_HANDLED (only 4 times)
- IRQL error is mostly caused by
- atikmdag.sys - ATI Radeon Kernel Mode Driver (6 times)
- ndis.sys - NDIS 6.20 driver (3 times)
- usbport.sys - USB 1.1 & 2.0 Port Driver (3 times)
- Rt86win7.sys - Realtek 8101E/8168/8169 NDIS 6.20 32-bit Driver (3 times)
Reading up on google results for BSODs on each sys files lead me to think it's a problem with either:
- corrupt drivers
- corrupt memory
- fried USB ports
- failing hard drive
- dying graphics card
- dying power supply
- dying mother board
I ran memtest for over 24 hours with no errors, and I've reinstalled virtually all the drivers I could think of. In regards to my graphics card driver BSODs occur with the latest driver and accompanying software as well as the version prior to it. Windows Updates are all up to date including the 'BlueScreen fixes'.
Here's a shot of all BSODs via BlueScreenView since July:

Could someone, seeing the combination of sys files in question, simply direct me towards what could be causing this. I can't afford to rebuild a new system nor try replacing/unplugging single components and just wait for that 'time of the month' to see if it were the cause.
My setup
- Windows 7 32-bit (installed in June)
- ATI Radeon HD 4850
- 2 GB Kingston stick
- Intel Core 2 Duo E7500
- MSI G31M3-L V2 Motherboard
- Avast! Antivirus
I have not reformatted the machine and would like choose to do so only as a last resort (given the amount of time it would take for backing up and setting up software and settings again).
Update: (7 Nov)
I replaced the memory and after a day of use, within minutes ran into a whole set of new BSODs MEMORY_MANAGEMENT, BAD_POOL_CALLER and on 3rd restart Aero refused to turn on. Pulled out the the graphics card and went into Safe Mode but ran into yet again another BSOD (the original IRQL_NOT_LESS_OR_EQUAL).
I fired up a Fedora 11 Live CD to ready a reformat. And while backing up data, Fedora suddenly froze up. It was without a doubt a hardware issue, a reformat would just not have fixed it.
I have now transported everything, except CPU (couldn't find thermal paste), to a friend's spare motherboard and installed a fresh 32bit Windows 7. If I don't get a BSOD within a month, it was the motherboard.