It sounds like it is your drivers. You need to run driver sweeper to clean out all of the old drivers. Then need to install the latest drivers which is 285.62. When I updated to this one my system started acting the same way.
So I rolled my driver back to the 280.26 and my 550's have worked ever since. So I will give you the link to a driver sweeper and the link to Nvidia drivers all the drivers. I hope this helps and good luck to ya.http://www.piriform.com/http://www.nvidia.com/Download/Find.aspx?lang=en-us