Computer Restarts When I try To Play..??

[dipwet]

Everytime I open up Steam and click the game I want to play the screen goes black and then my computer restarts. HL2, CS:S or DoD:S they all give me the same problem. I updated my Drivers but that didnt work. can anybody help me please ?
:cheers:

 

[Beerdude26]

Here are some troubleshooters :
First link
Second link