Vista is slow/unresponsive with heavy cpu load

Basically topic describes it, Everything was fine on my computer till about 2 days ago, when everything became sluggish. My processors load is always at 50%, and the screen hiccups, and it just feels like is having trouble.

when you control+alt+delete instead of fading into the windows thing, it goes totally dark, then it flashes, then after selection something, goes dark again.

startup is slow also....

Safemode is fine, I've reformatted and it worked great, until I install a windows update, then it goes back to the problem. I'm not sure if I don't update I won't get the same results.

I'm on a custom built rig:
e8400 3.0 ghz Dual Core
9800GTX 512mb
2 G Skill RAM
Gigabyte P35-DS3R

Well heres the funny thing.

In task manager, I'll be at a 50% load, but system idle will be at 90, and nothing else will be above 4.

I found after installing an nvidia driver, that could be my problem, but I'm unsure still. I'm starting to think all drivers or updates

After uninstalling said nvidia driver, things have returned to normal. I'm about to install an older version that I know worked, But im worried my 9800GTX may be bad now.