My computer has been working just fine for months when suddenly one day when I was playing an MMO, the game window (not the desktop) started to have weird fuzzy graphic artifacts and static lines. After a minute the entire computer froze up and required a hard reset. Looking inside, I realized my only casing fan (other than the CPU fan) had stopped working due to dust chokage (I always leave my casing open on the side).

Even after washing off the dust, the fan still seemed rather sluggish so I let the computer rest for an hour, then aimed a powerful ventilator fan at it. The same problem still crops up - works fine for hours when just surfing net/word processor - but within a 5-10 minutes of running any video or graphical game, it goes crazy and BSOD on me.

I have updated the Nvidia 9800GTX drivers today, but nothing has changed.

Any advice would be much appreciated. Thanks in advance.Do you have an adequate power supply for your system? What are the specs of your system?
Have you tried monitoring your system/CPU/graphics card temps with http://www.cpuid.com/softwares/hwmonitor.html ?

If your single case fan has "stopped working" due to dust chokage, I strongly suggest you take your entire PC out for a good blowing out with compressed air; just a suggestion you can use a paintbrush for those hard to reach crevices on the motherboard. You never know where dust can accumulate. Also, take the shroud off your graphics card (if it has a shroud, the reference models with the blower fans do), take the heatsink off, give it a good cleaning, reapply thermal paste.

If you're adventurous enough you can do this:

Unplug the blower fan.

If your temperatures are normal by now and PC is still BSODing, its time to do a hardware stress test, just in case there are other components responsible.

IntelBurnTest for your CPU: http://www.softpedia.com/get/System/Benchmarks/IntelBurnTest.shtml Run it on Standard, 1024MB, for 10 passes. If your system gets unstable in the process it will tell you.
Furmark for your Graphics card: http://www.softpedia.com/get/System/Benchmarks/FurMark.shtml Run the 720p benchmark. If your system gets unstable there will be artifacting on the screen or the picture will freeze. If your temps look like they are about to skyrocket above 90C, STOP.
MemTest86+ for your RAM: http://www.softpedia.com/get/System/Benchmarks/Memtest86-plus.shtml Run it for 10 passes. It will indicate a read/write error if your RAM is faulty.

If you BSOD on Furmark, even with acceptable temperatures (below 85 C) then I would take the graphics card out, and use your integrated graphics to play a game or two. No crash? That means your beloved 9800GTX is at the end of its lifecycle.Wow, appreciate the comprehensive reply.

I am using a CoolerMaster 650W PSU, which I'm pretty sure is sufficient for a computer which I mainly use for video/media, mid-range online gaming and Internet.

- Gigabyte EP-43 Motherboard
- 4Gb RAM
- 3x SATA HDD / 1x DVD-RW
- about 2+ years old

Thanks - I will give these solutions a whirl and get back to you when one of them works So I've tried the cpu/gpu/memtest options (with the recommended programs), but they came back without any problems. As far as they could tell, the system was fine.

One thing I did find out was the problem might be related to the Direct3D (d3d) driver which works normally UNTIL I run a game.

Without my ventilator fan cooling the GPU, the game seems to work perfectly fine for 5-10 minutes before going crazy. With the fan on max, I have run it for an hour without problems. I've only tried it once with the fan on max so I'm not sure if it definitely related to the fan-cooling.

Now I'm finding I don't get the BSOD anymore but it just shutdowns the game (after a few minutes of crazy graphics) and boots me back to the desktop. And I discover my Direct3D stopped working after the error - using dxdiag to check d3d will just keep returning errors.

Trying to run any game will return errors as well. Any idea why this might be the case?

Have you tried running some DirectX applications in windowed MODE, instead of fullscreen?

This time, run the Furmark Burn-in test. Let it run, without your ventilator fan, and I'm almost 100% positive it will crash within 5-10 mins. Post back about how it crashes (BSoD? D3D driver crashed?) and after how long and at what temperature as indicated by Furmark.

If it doesn't crash after ~20 mins, I'm thinking its the graphics memory. Artifacting and sudden changes in textures is usually CAUSED by failing graphics memory. Furmark doesn't stress the graphics memory as much as games do. It stresses the core far more than games, though.
Run this:  http://mikelab.kiev.ua/index_en.php?page=PROGRAMS/vmt_en Video Memory TESTER. Without your ventilator fan. See if it returns errors. If it does, then run with your fan. Still returns errors? Faulty memory. Does not return errors? Problem with VRAM cooling.

If it crashes, reboot and run the burn-in test with the ventilator fan on max. If you see your temperatures stabilize, wait for 10 mins. If no crash, then play a game or two. Still no crash? Run VMT, with the fan still on. Does not return errors? Problem with VRAM cooling.

Also, what is the manuf. of your 9800GTX?