Display and login problem after installing CUDA toolkit 6.5 for ubuntu 14.04

гm using workstation T5500 with graphic card Quadro k5000. I installed the graphic драйвер using

sudo add-apt-repository ppa:ubuntu-x-swat/x-updates
sudo apt-get update
sudo apt-get install nvidia-current

The computer then could recognize the graphic card. Then I installed the Cuda toolkit v6.5 using

sudo dpkg -i cuda-repo-ubuntu1404_6.5-14_amd64.deb 
sudo apt-get update
sudo apt-get install cuda

After i reboot the computer, i could not login and the screen resolution changed.

Заметьте: i got не problem installing Cuda toolkit v5.5 through

sudo apt-get install nvidia-cuda-toolkit

Хоуп to get support from you

Best regards