initial crash & npc crash

Processor: Intel® Core™2 CPU 6320 1.86GHz 1.86 GHz
OS: Windows 7 Ultimate Service pack 3
RAM: 4.00 GB
Video Card: ATI Radeon HD 5700 Series (5770)

On startup everything is fine and even when I load up a map; the problem becomes apparent when I wait a few minutes and it just crashes or more annoyingly when I spawn an NPC Prop, normal objects work fine, yet these whether dolls or animated crash regardless. I tried different settings and it still has been the same results and reinstalled my game, I am unsure what to do next.

I have no addons installed and games currently available to me are CS:S, HL, HL2 (all eps), TF2, Portal.

Well, other than windows 7 and 1.86GHz, I see no other problems.
I just hope that is window 7 32 bit. 64 seems to lag for some people.
As I said, 1.68GHz is rather low for gaming.