1. Run Registry Editor and navigate to: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\[Extension] 
2. Expand the [extension] key and choose UserChoice key and delete all its sub keys 
3. If it doesn’t work, delete the UserChoice key itself.
4. Restart PC

NOTE: To revert back to all default file association as we get after fresh clean installation of Windows Vista, We can delete all sub keys under FileExts.

Daca problema persista inseamna ca aveti virusul svchost.com si va recomand o formatare si izolarea celorlalte partitii pana instalati un antivirus.