Just in the last 4-5 days Task Manager does not load. I click Control/Alt/Delete and Windows Security comes up. But when I click on Task Manager nothing happens. When I type taskmgr.exe into the Run box and click enter this error message comes up--"Another program is currently using this file"

I am running W2K

Norton antivirus is up to date--last full scan 6/26.
MS Antispyware up to date last scan 6/25
Lava Ad Aware up to date last scan 6/25
Spybot up to date last scan 6/25

Any ideas?

Thanks in advance,