Computer Restarts Playing "Some" Games

It has happened in Left 4 Dead Mostly, and World of warcraft. Other than that im actually fine. First my Computer Specs.

I have the Gateway DX4710

Processor: Intel Core 2 Quad Q6600 (2.4 GHz) ;
RAM installed: 6 GB DDR2 SDRAM ;
Hard drive: 640 GB Standard
Video Card: ATI RADEON HD3650 (Updated Drivers Manually, cant find it on the ATI Website but it says up to date when i do it through hardware.) i downloaded some supposed fix but yea that didnt workout

Next up is some explanation

When im playing Left 4 dead i experience no problems at all the game runs beautifully.. its just after like 20 minutes it happens at the exact same time usually my computer just shuts off and reboots. after that i press start windows normally and i can go on play Dota orrr CS or anything for as long as i want. This problem happens in WoW sometimes too but not as often as Left 4 Dead.. I toned down the graphics although my computer handled the highest settings quite nicely, but i wanted to see if it was overheating and the inside seems ok. Although one time as my computer restarted i heard like a grinding from the inside of my computer and i shut it off immediately to prevent damage and i opened the case and checked for any loose pieces.. i figured a wire was hitting the fan and moved it and haven't heard it since but IDK... Anyways this problem is SUPER annoying cuz i just bought the Computer and the place we bought it from only has a 7 day return policy.. Yes 7 Days.. but im sure gateway can offer some kind of thing..

IF you guys have annnyyy suggestions lemme know..IT happens in WoW too and WoW is my primary game so i have to fix this.. i can live without Left 4 dead.. although its amazingly fun.

I checked the problems and solutions thing and it contained no problems or solutions.

Sounds like it could be a driver issue...try going back a driver or 2...newer does not always mean the best.
You could have a bad stick of Ram or the fact you have 6gb of ram tells me your running Vista ???
I would Google WOW/Left For Dead Vista Probs

Might even be the PSU...most prebuilt comps come with a crap Power Supply

The only other thing I can think of for you to do is

Go To:
Start / Control Panel / Sytem / Advanced / Start Up & Recovery /Settings and uncheck the Atuomatically Restart Button.

This way you will be able to see the message.
Take a pic and or write down all them #'s.
The Guru's here will be better able to help with a solution

P.S. I would also notify the Seller you are having these probs and your looking for a solution...might extend your 7 day return policy

thanks alot man your a G in my book, ill be going step by step to see whats up, i just turned off automatic restart.. will update sooner rather then later. after that ill try the power supply.

You should test it with a Digital Multi-Meter...Just leave it on and watch the restarts ...when you open a game etc,etc.

If your not sure how to use one LOOK HERE

So Far i have not had 1 restart after taking off automatic restart playing wow.. the real test will be Left 4 Dead tonight... posting later.. thanks all!! and thanks for the info about the multimeter

If it happens to have the same problem then it is defnintly overheating, because I have a pretty decent laptop, and whenever I play l4d this ussually happens every hour until I placed an external fan under it, is your processor getting good ventalation? are you experiencing slow game play before it restarts?? If not then the last thing it could be is drivers. Anyways I hope I helped. Happy Fragging!

no i made sure my computer is vented properly, also my restart problem in World of Warcraft Fixed but something interesting happens.. after about 1 hour and a half of gameplay wow freezes up real quick, then it minimizes and a message pops up . "Display driver stopped working but was sucessfully recovered" and then i maximize wow again and its just fine, when i play left 4 dead now.. the computer still restarts after a certain amount of time. im thinking that the driver is crashing and not recovering so its restarting but i took off automatic restart, something crucial is happening..

You can always use NGO ATI Optimized Driver

NGO