Hello,
If you are not able to open regedit.exe, try renaming regedit.exe to regedit.bat and then open it.
In order to view and change the extensions, the "Hide extensions for known file types" options should be disabled in explorer.
Also, if you are unable to open taskmanager, try googling for Nirsoft's cprocess utility. This is better than taskmanager, since it gets a better handle over the processes than the taskmanager does. This tool will show you all the processes running and just kill the malicious one. You'll be able to identify the malicious easily.
Thanks
Raven