First of all
Scan your system with any good Spyware/ Malware softwares. If it works then no probs...
Other try this..
Taskmgr.exe is a protected file.
Go to C:\Windows\System32\dllcache and find the copy of taskmgr.exe, double click the file to see if it brings up the Tasm manager. If it does, copy that file to the System32 folder, overwriting the corrupted file.
