Half Life 2 not starting.

After I finished installing hl2 I went to the steam tab to open up the game. But when i click hl2 on the game list It starts to unpack some files needed to play and my comp frezzes and i cant move the mouse and then my comp restarts any ideas?
My specs are

Windows XP pro sp1
Radeon 9800 pro 256mb
Gigabyte k8nsnpro
Sound Blaster Audigy 2 value
600w psu
1x 160gig western digital hdd-master-
1x 5 gig maxtor hdd-slave-
Athlon 64 3000+ 2.01ghz

 

Sounds Like Something In Windows Just Messed Up, Did You Get Any Error Messages When It Locked Up? I've Had It Windows Would Just Reboot My Computer For No Reason (No Error Message Or Anything).

 

No message or anything just froze and rebooted.

 

Do You Have The Latest Drivers For Your Hardware?

 

Sadly, the update didnt help. And yes I have updated everything i can think of

 

Do Have Any Problems With Other Games Or Is It Just With Half Life 2, If Your Only Having Problems With Half Life 2 Take It Back To The Place You Bought It From And Exchange It And See If That Works.