Boot to safe mode, device mgr. and remove all references to nvidia, and while you are there look for other double entries and if you find any remove both not just one. The reason for going to safe mode is you will find a lot more entries then you will in windows.
One last thought I had a machine that I dn/ld so many nvidia drivers to that it finallly gave up so as a last resort I went into the registry and deleted the ENUM key and rebooted and let it reinstall all the drivers + went to nvidis.com and got the latest drivers, not only did it fix the video problems but the system ran better then ever.