Problem after installing CUDA toolkit

I’m working with DSSTNE engine that needs CUDA Toolkit 7.0 or higher, but after I installed the CUDA, I could not log into ubuntu (low graphics problem).
I have GeForce GTX 260 and Ubuntu 14.04, anyone knows this problem? CUDA toolkit 7.0 is incompatible with this GPU?

Correct, CUDA 7 is incompatible with GTX 260