I had the same problem. I could use the task manager to start system restore but only got an empty window so could not return my registry to good condition. The same happened when in Safe Mode.
I ran System restore from the task manager, try this first, the file you need is c:\Windows\System32\Restore\rstui.exe.
As I failed to see anything in the window I followed the instructions in the Microsoft Knowledge Base to restore my system to fully working.
http://support.microsoft.com/default...;en-us;Q307545
Good Luck.
Magmell