Brando

when its in sleep mode? When I leave my Windows 7 computer alone for 20 minutes it goes to the default screensaver. Then when I come back, and I move the mouse it loads fine until I click on my user then the moniter goes black and it freezes. I pressed almost all the buttons on my keyboard and nothing even happens. So I always end up holding the computer power button to turn the entire thing off. This has been happening a lot lately and I dont know what to do. Please help.