CPU jumps up to 100% now, not before

[DABhand]

I didnt have a chance to read all the way through that, but do you have an Asus Motherboard with a Via chipset (from 2yrs ago or more?)

If so it could be that motherboard doing so, some earlier Asus motherboards came with the wrong settings to detect the CPU temperature correctly and throttled the CPU when it thought it was overheating.

If not, then try defragging your hard drive/s. And make sure your DDR Ram is of the same speed. You cant have say DDR 266 and DDR 400 at the same time.