Windows 7 extremely slow

My computer has been getting progressively slower over the last week or so. I've run Ccleaner and Avast, run memory checks, reduced the number of startup programs, but nothing works. Task Manager > Processes will show zero CPU activity and it still chokes. I've also restored to an earlier time with no joy.

Sometimes I open a program (Chrome, Firefox, Ccleaner, etc.) and it takes 20 minutes or longer to open. Even Safe Mode is sluggish.

I'm using:
Win 7 Pro, sp1
2.67ghz
6gb ram
1tb HD w/715gb free

Help please.