Depending on what program you use, you should be able to tell it to set of a small alarm or 'pling' when it goes above a certain temperature. I could even make a log of the temperatures of my CPU, both my GPU's and my Motherboard at the same time, right up until the computer crashed.

That will at least tell you if that's the problem. If that's it, I'd rip the rig apart, clean out all dust like a mad cleaning lady, and then see if I can't get better cooling. Simply getting two new (massive) chassi fans to help clear the air inside the rig helped my case, going from a crash every hour to being completely crash-free since then.

My can of air has this tube that you can stick into spaces to clean. Would that work? I don't want to take a chance with breaking my PC.

Look, I had the same problem. My 8800GTX was heating my casing.

My recommendation would be to open your casing to let the heat come out and you could do what I did; place a large fan (a fan you would use in any part of your house) right next to your casing.

Its not the best solution but its a temporary one until you can get better venting for your PC. Removing the dust is a good start but I doubt it's gonna be enough.

Bottom line is; you have to cooldown your casing.

Would adding a new powerful case fan or replacing the old one do any good. I was looking on Newegg the other day.

I'm using a Gateway FX 6800 PC, so it's got a better case than most PCs (has a side vent as well as back vents, but this also sucks dust)

Opening the case may be a temporary, but like you said, not the best. If something happened. Water cooling would be a last resort, but if the pipes are faulty and it spilled, you are absolutely fucked.

Thank you all for the help. Hopefully I can get this all sorted out soon.

I'm still having issues. Even on Medium settings, it still crashes. I don't want to open up my case and take everything out, as I don't have a special wrist strap. I really need to know if an ATI Radeon 4850 is good enough to run Crysis, because I may have to upgrade.

well, what are the specs exactly? the box tells you the minimum requirements to play so work it out. but a insufficiently powerful graphics card or processor wouldnt cause the computer to shut down. it might cause the game to crash, or at least slow down and stall/stop responding, but it wouldnt shut your computer down.

the only thing it can be is overheating or a bug/virus/error etc telling/causing the comp to shut down

if you dont want to take it apart yourself you can always send it to a certified repairer and get them to do it

I'm using a trial of AVG to do so to see if this works. I think there may be a virus increasing the work of the graphics card. If only creation of viruses was punishable by 20 years in federal prison... Though that wouldn't work as a lot of viruses come from Europe.

The issue is overheating over extended play sessions, not viruses.
I played through the entire game of Crysis in a single sitting, we're talking 9 straight hours, and the last part of the game crashed time and again. I left it for 30 minutes, letting my PC cool down, and returned to a crash-free game. The amount of work your Video Card and CPU are required to do for Crysis is quite significant; don't underestimate the processing power requiring for the visuals.
My suggestion would be to play the game in short bursts, on lower settings, or open the side of your tower and sit a personal fan to blow cool air directly onto the components.

Best of luck.

The game crashes in less then 30 minutes right when I play immediatly after turning the computer on. Also, game that I have that never crashed before, such as UT3 and Assassin's Creed, also crash.

I'll try the open case, but my parents would get freaked out about it.

So Crysis just crashes the moment you start it up, or does it take a few minutes first? Have you used the tool for your video card to check the Temp of the card?

I assume you've patched the game and aren't using a cracked EXE?

I haven`t read every post written here, I don`t know if this has been mentioned yet.  I tried running vanilla crysis with an 8800gt and had some similar problem`s.  I would reccomend trying this mod.

http://forum.strategyinformer.com/showthread.php?t=21685

It`s a performance improvement mod.  I could barely run vanilla crysis at med settings.  After installing that mod, High settings at a pretty smooth frame rate.  It improves performance and visual quality, I was very impressed with it.  It turned an unplayable game into a great experience. 

I just read your last post about UT3 and AC crashing too.  Hmm..I don`t know what to say.  Take the above advice and open the case, Make sure there is not dust or pet hair clogging the fans or airflow.

EDIT

Have you downloaded the Catalyst Cotrol Centre(CCC)?  It`s normally packaged with the AMD/ATI drivers.  Use that application to make sure the fan speed is set high enough on your GPU.

Good Luck

I tried to clean out the CPU heatsink using compressed air, but I lost the access tube. I would guess that there might be some dust in between each metal sheet, but it was impossible to reach in there. The case feels hot where the CPU, so I think my CPU is to blame. You'd think an i7 could do better...

I found the ATI overdrive that has fan speeds, but everything is greyed out. I also may have made a mistake when I redownloaded CCC, because it thinks I have two graphics cards when I have only one, and it says that I have a 4870 when I have a 4850. It also said that my card usual runs at 86 degrees (not sure if its F or C)

It crashes after about a half hour of play.

I ran AVG, didn't find anything bad.

All in all, it seems that I might need some professional help with this issue.

Oh god I hope it's F. If it's C, I'm surprised your card didn't burn up like an ant under a magnifying glass! You'll need to try and confirm this, it should be detailed somewhere.

The fact that it crashes after a particular time frame rather than at a particular occurance means two things; it's either heat related - this is where I'm putting my money - or it's memory related. I experienced the same situation, as detailed above, and so I believe it's heat related. When it crashes, is it a clean crash to the desktop, or do you receive an error message? Does your computer freeze up?

I'm afraid you might need some professional help in terms of cooling. Research possible solutions or people who've solved a similar issue and try and talk with them about it, to make sure that your issue is the same. Don't spend money on additional cooling if you don't have to. Not much more I can say, sorry mate. Best of luck!

I explained it before. The screen goes black, and the computer shuts itself off.

Sorry, I must have missed that part, but it certainly answers your question: this is a safety feature of your hardware, to prevent it from burning out when over-heating. You need additional cooling on your components.