Blender cant see GPU

Hi

I have a prob, with GPU rendering, i was rendering with GPU like yesterday, but all of a sudden it switched to CPU and when i go to Us Pref/System there is no selection between GPU CPU there’s only CPU. I have all Drivers up to date. Plus i have 650 GTX with all supports needed 4 GPU rendering ( in nutshell it was rendering with GPU perfectly las night). . . PLS HELP AS FAST AS POSSIBLE!!!

I’m assuming you’re on Windows?

Is this the same GPU that you use for Windows (do you have only one GPU in your system?)

Did you change Blender versions yesterday? Or upgrade your Driver?

Is your GPU overclocked? Does CUDA work ok? (you can get a nice test program here: http://sourceforge.net/projects/cuda-z/files/cuda-z/0.6/CUDA-Z-0.6.163.exe/download).

Did you try to delete your settings and start fresh? (Take a backup of your settings first)