I have the same problem. Upgraded via DVD from 8 to 9 with no problem. Then went from 9 to 10 and the problem started. At first I thought it was a problem with the nvidia driver so I switched to the second console screen and tried rebuilding the driver using the nvidia command line utility. Even as root the process faild and I did not have permission to run things like "shutdown -h now".
The blank screen behaves this way. After the last script in rc5.d runs the screen flashes rapidly quite a few times and drops to a black screen with blinking rectangle cursor. You can move the cursor with the mouse. You can highlight parts of the screen with the mouse. I agree with the previous post that this is not a shell. It is possible to type characters but CtrlC,CtrlD,CtrlZ have no effect.
Has anyone seen this before???