if you ask me, the rig isn't the issue here if it runs fine but with these massive spikes. of course it's not ideal for running css but that shit came out in '04, he should be fine. also since it's been working for some time...it's not the rig itself. it could be:

IF it ONLY happens in css:
1. some corrupt data, reinstall would fix
2. some rate issue, check them
3. skins? i dunno, try removing them.

IF it happens in other games as well:
1. video driver problem, update them, or if you updated recently, downgrade them
2. network adapter issue, try using ethernet if you're on wireless, or vice versa (also check drivers on this)
3. ay other driver...those things can be bitches. check chipset, bios version, etc

if i think of anything else i'll post up here but if it just started acting up, it's not the hardware, it's the software.