Crash Loading save/new game HL2

[skeng]

OK i downloaded the orange box set of steam last weekend for 5.99 i installed half life 2 and played it for about 2-3 hours. i came to the computer today to have another go and now for some reason the game just crashes and takes me back to my decktop i am unable to load any save game or even start a new game. i havn't installed anything new or even used my computer since i last played half life 2 so yeh i dont know please help

spec
Vista SP1
AMD Phenom 64 9950 Q-core 2.6GHz
4GB RAM
Nvidia 512 somthing.......?

 

[AciD]

Hm. Is your Vista 64 bit version?
Try Verifying GCF Cache Files.