Total black screen after boot up every time

Hello,
My laptop, sony vaio (piece of crap), recently got infected with a virus that jacked it up really bad. I FINALLY got most of the stuff back to normal except for some reason at boot up, after I log on, the screen comes up totally black. No desktop. However if I start task manager I can go to file and new task and type "explorer" and then all of a sudden the desktop appears. what the heck is going on? any help is much appreciated!!