All my games are crashing!

[OverThrownBaby]

I recently finished building my computer from the parts I received for Christmas. First day it seemed everything worked perfectly. No lag in any game and no sign of graphics problems. Now though after getting more games it seems that just about all my games are crashing.
Here are a list of the games that are crashing and how they crash.

Team Fortress 2: Randomly Exits from 20-60 minutes of play with the error hl2.exe has stopped working.
Gmod: Randomly Exits from 20-60 minutes of play with the error hl2.exe has stopped working.
CS:Source: Rarely Crashes, but it has after 2 hours before.
Arma 2 OA: Crashes Fast 3-20 minutes, ussually freezes up and my computer automatically restarts itself.
Crysis 2: Crashes Fast 5-10 minutes, Blue Screen.
Planetside 2: Only occastionally crashes after 30 minutes. Exits To Desktop.
GTA4: 30-60 minutes,Randomly Exits To Desktop

Please note that before my games ran perfectly, so I'm thinking it's not hardware.

My Build:
Processor: Intel i5 3570k http://www.newegg.com/Product/Product.aspx?Item=N82E16819116504&Tpk=3570k
MOBO: ASUS P8Z77-V LK LGA 1155 http://www.newegg.com/Product/Product.aspx?Item=N82E16813131837
RAM: G.SKILL Ripjaws X Series 8GB http://www.newegg.com/Product/Product.aspx?Item=N82E16820231455
GPU: EVGA Gtx 560ti (link might not be the exact one) http://www.newegg.com/Product/Product.aspx?Item=N82E16814130604
Power Supply: Cooler Maser Silent Pro 800W Gold http://www.newegg.com/Product/Product.aspx?Item=N82E16817171057
Hard Drive: Seagate Barracuda ST1000DM003 1TB http://www.newegg.com/Product/Product.aspx?Item=22-148-840&SortField=0&SummaryType=0&Pagesize=10&PurchaseMark=&SelectedRating=-1&VideoOnlyMark=False&VendorMark=&IsFeedbackTab=true&Page=2#scrollFullInfo
SSD: Samsung 120 gb If I find the link I'll put it here.


I have only really looked at the CPU for temperature problems. After playing games for about an hour and then crashing I quickly checked the temps and they were at a cool 31-35 Celsius.

Please Reply. I will attempt to work with whatever you can give me. I really need to solve this.

 

[Guest]

Are these games ALL through Steam? It seems like a Steam issue.

 

[Jt_for_life]

Ya definitely sounds like a Steam issue. Here is a related post that might help you. Original post by Coolboy 4531 on the Steam forums.

"This happened to be exactly as well! For like 10 times each day..

Don't worry I got a solution for this! I hope this actually works.

Validate your TF2 files. After you complete. COMPLETELY quit out of Steam. If it validates again wait for it to go to 10%. Cancel it and defrag it.

Validate = Verify. Defrag = Defrag.. ?

These settings can be found if you right click "Team Fortress 2" and press "Properties." After that press "Local Files" and choose the ones. Validate = 4th one. Defrag = 5th one.

Now, after you finish defraging it. Completely quit out of Steam. Reopen it. You should get no errors or anything.

Open TF2 and IF IT VALIDATES. Wait for it to go to 10% then press Cancel and reopen it. IF IT DOESN'T VALIDATE. Play as is.

It never crashed again after that."

 

[OverThrownBaby]

Best answer selected by OverThrownBaby.