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.

 

[monu_08]

have u storing or installing the games on ssd drives rather then hdd just asking because u may be put all games in 120gb drive so or have u ever update the graphic
driver i suggest update driver too http://www.geforce.com/

 

[smorizio]

start with the simple stuff. make sure your mb has all of the updates for the bios. there few for memory and usb and windows 8.
in the bios make sure you have xmp profile turned on for your ram. also check if your running mb in standard or over clock mode.
in the asus mode overclock it changes the ram to cpu timing from 1:1 to 1:5. try resting your setting back to factory stock.
on my gaming rig i found the new nvidia drivers were not spinning the gpu fan up to speed under load on my 560ti video card.
i downloaded asus afterburned and set a temp profile to make the fan max out at 50c. one other issues it could be is one of the games could have put older version of direct-x on your system. i would downlod the june update or last full online download and do a clean install.

 

[JamesSneed]

Also if you have anything overclocked CPU or GPU revert them to stock then test.

 

[OverThrownBaby]

Best answer selected by OverThrownBaby.