may need to uninstall the driver and reinstall it ? may need to reconfigure the driver install for sp1 ? I assume your using windows 7 .
sp1 may of added something just try a fresh driver install and see being it was working fine up till sp1 was added
get your driver from here
http://www.nvidia.com/Download/index.aspx?lang=en-us
I would start with a custom install and uncheck all but the driver and only install it and test the go back and physx if needed
[all I install is the driver ] don't need any of the gimmickware , but that's your call on what you want
never use device manager for NVidia it do driver work its not supported [page 22 of release notes]
http://us.download.nvidia.com/Windows/376.19/376.19-win10-win8-win7-desktop-release-notes.pdf