This happened in Avast 7.0.1407, after a day, and i have updated from the interface of avast, it gave a black screen and did not load the windows 7 after the welcome screen.
I had to get into safe mode and use System Restore to reload windows.
then I went back into safe mode to uninstall avast 7 with the avast uninstaller.
I installed 7 again, let's see if the problem happens again.