Start it in safe mode and reinstall the display adapter drivers.
To start in safe mode restart the computer and after the screen showing the computer information start pressing f8 and keep pressing it till you get the start menu. Choose safe mode and continue to boot.
Once the computer is booted up in safe mode, right click on my computer and click on properties. Click on device manager tab, scroll down to the display adapter, click on the plus sign and then high light the name of the adapter, click remove, reboot and when it reboots it should install the right drivers.