About a week ago I updated my computer to Windows 7 Ultimate. Since then, 90% of the time, when I boot up the computer a black screen appears on my screen and no desktop shows up. I can't do anything like get to to a task manager but the computer works fine in safe mode. Strangely, if I leave the computer for a couple of hours the black screen disappears and everything works perfectly.
Any help with fixing this problem would be hugely appreciated. Thank you