computer restarts

[bsf1209]

ok i just bought HL2 the other day and installed it on my computer it was the game of the year edition the setup went perfectly and steam loaded great. so i went to go play HL2 I got to the part at the begining where your inside of the apartment building and u walk up the stairs and theres a guy peeking out a door that says "hey over here" when i walk towards him my computer restarts it does it everytime..i upgraded my graphics car which is a s3 pro savage...HL2DM, CSS, and HL1 work fine but they do lag alot can someone please help me or tell me if I should buy a new graphics card.
thanks

 

[Tomarru]

You should buy a graphics card, nuff said
To me a S3 doesnt even count as a 3d accelerator, it might speed up windows a bit but thats about it.

 

[clairelovestlc]

when i had the problem it was due to overheating, not sure if ur experianceing the same problem.