Whenever playing left 4 dead 1 or 2, after about an hour or so of solid gaming my computer likes to just completely crash like shut off along with my everything else (keyboard, monitor, mouse). If i turn it back on and boot it back up and get back in game I can only play for like 20 to 30 mins before it crashes again. Real fuckin gay. Anyways my specs are:
Intel e8400 cpu (3.0 ghz)
4 GB of RAM
650w Power supply
XFX 750i SLI FTW mobo
XFX Gefore 9800GTX+ vid card.

Any suggestions or ideas why this might be happening would be much appreciated.

Does it only happen with L4D, or does it happen with other games as well (this assumes you play any other games)?

http://www.techpowerup.com/gpuz/

Get GPU-Z, go to the Sensors tab and first check your GPU temperature while not playing any games, preferably after booting your system cold. It should be anywhere from 30-55 without a load. Then check "Log to file" and "Continue refreshing...". Play a game that makes your computer crash, and then go check the log. If the last temperature readings were over 75c, your video card is probably overheating.

If you say your monitor goes off (not in standby mode) then you either have a bad power supply or your outlets cant handle as much power as your computer needs. Try a different power strip.

Check CPU and RAM with Prime95 (http://www.mersenneforum.org/showthread.php?t=2). Let it do a full test. If the test fails within a few minutes (some people let this run for hours but unstable hardware will crash pretty quickly) or your computer crashes, your cpu or ram are unstable. Reduce any overclocking you've done.

Whenever playing left 4 dead 1 or 2, after about an hour or so of solid gaming my computer likes to just completely crash like shut off along with my everything else (keyboard, monitor, mouse). If i turn it back on and boot it back up and get back in game I can only play for like 20 to 30 mins before it crashes again. Real fuckin gay. Anyways my specs are:
Intel e8400 cpu (3.0 ghz)
4 GB of RAM
650w Power supply
XFX 750i SLI FTW mobo
XFX Gefore 9800GTX+ vid card.

Any suggestions or ideas why this might be happening would be much appreciated.

Peeps and I had the exact same problem on the only fix is usually some type of hardware replacement. My graphics card would overheat so I ended up having to get an entirely new one along with a cooling sleeve (sleeve was probably overkill).

What kind of PSU is it? If it's a no-name brand that you got a couple years ago there's a realistic chance of it breaking down.

Yeah I'm running the stock cpu cooler on the cpu atm so that could be an issue. But in game my gpu and cpu temps never rise above 65C which is still pretty high. Im running all this a HAF 932 case so i def have airflow. And the PSU is an Ultra 650w.

Oh and yes its only in L4D. Doesn't happen to me in MW2 or CSS.

you messed with the drivers on the vid card yet or rolled em back a ways?

I've updated to the latest version of the driver as far as i know.

Do you have multicore rendering turned off/on in all games? Or is it different in MW2.

Also try backdating your drivers a patch or two, see if that changes anything. I'd also clear your launch options, as that might have some random issues.

One last thing that probably would have no effect, is setting your L4D2 to a high priority in your task manager. It might make it so your computer stops dicking around and focuses on your game.

i was having similiar problems as well, have you reinstalled the game? my problem turned out to be the card, and as soon as i changed it problem was solved. start undoing everything you have from your cables to minimal game settings. l4d2 is a resource hog and very intense on what it does to your pc. good luck.

Yeah I was def planning on the reinstall for sure munky. Ordering new cpu cooler and Win 7 64 bit today. So when i reformat to win7 is when ill do the reinstall. Managed to play l4d2 last night for about 2hrs straight no crash.

I'm with Jerkstore, 9800 Gtx has a reputation to overheat, but also like said earlier you probably want a better cpu cooler then the stock one. Also Case fans can help effect your whole pc make sure you have both intake and exhaust at the least.

that fan omerta put up in my other thread in here has really helped out as well as removing the card case itself.