I checked here: my task manager (Windows 7 Pro) shows 0% CPU used if I do nothing. So something must be wrong with you. But you don't give any indication what it could be.
You don't tell anything about the machine, but if it is the one we reviewed in http://reviews.cnet.com/Dell_Dimension_8400/4505-3118_7-30919189.html my guess is that it is some 7 or 8 years old. With 512 MB of RAM it can't run Windows 7. Did you run Microsofts upgrade advisor?
Considering the useful life span of a PC is some 5 years, it would be best to buy new PC. It's much cheaper than the $3.099 mentioned in that review that you payed back then. You'll find a quite reasonable one for $500. If you're 65 now and plan to become 90 and buy a new PC every 5 years, I can see you buy 4 other PC's after this new one.
The alternative is going back to XP via the system recovery options (recovery partition? recovery disks?) that your Dimension came with. Then it will be as it was when you bought it. Be sure to have a good backup (that is: two copies) of everything you don't want to lose.
Kees
I installed win 7 pro hoping for a faster log on and faster pc. win 7 uses 55% of my cpu just idleing. I try changing settings and the system will not let me change, not authorized! Power hungry and very intrusive. I cannot buy a better computer. I have a Dell 8400 Dimension. Hard drive crashed, upon getting a 500gig baracuda and win 7 pro, I cannot do the things I used to be able to do: write and games. 7 slows everything down. I was running xp. I cannot see buying a new computer at 65.
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