It's possible you updated the NVidia driver to a version that is not fully supported by your hardware. Each computer manufacturer has a "recommended" version to use, that is often not the absolute latest available from the video card maker. I would first try Madhur's suggestion of booting into safe mode, then rebooting into normal mode. Sometimes that magically cleans things up. If that doesn't work, then roll back to the restore point just prior to that video driver update.