Try the following:
Click on the following keys simultaneously: ‘Ctrl’ ‘Alt’ ‘Delete’
When Task Manager starts, go to the Processes tab
End ‘explorer.exe‘, if it is there
Now, click on the ‘File’ menu
Select: ‘New Task (Run...)’
When the ‘Create New Task’ prompt appears, into the Open field, type: explorer.exe
After a minute or so, you should be back at your Desktop.
Now, to replace the shell in Vista:
Save to the Desktop
Double-click on shell.reg
When asked to be merge the data, please allow it.
Retired - Doin' Dis, Dat, and slapping malware.