Cannot defrag on XP on any drive, cannot run Scandisk

Cannot defrag any of my drives (3 different drives on computer)...

Using Windows XP SP3. Just tried to run Windows defrag utility but get error "Disk defragmenter could not start" for all drives.

Have PerfectDisc defrag program and it also will not run (worked last week).

Downloaded some different defrag programs, none will work.

Have tried running defrag in safe mode, from Dos prompt, etc.

Cannot get ANY defrag programs to run. Have tried everything. Windows error checking will not work either.

Reinstalled XP SP3, still same issue.

Tried XP system restore. Lots of restore points from past month, but nothing happens after selecting restore date and clicking "Next".

WindowWasher will also not work now, just hangs.

Tried sfc /scannow, did not solve anything.

Everything else on the computer seems to work ok.

Help!

Thanks,
Tloke