Checked NVidia again, and it appears you are not using the latest drivers, latest drivers are 197.45
(8.17.11.9745), maybe you should dl them and see if the performance is back? The fact that your problems happen with non graphic intensive programs also make me think there might be a flaw, either in the drivers you are using, or something went wrong upon installing them, but no memory leak, more like Windows lost communication with the graphic drivers.