Why won't my computer display the taskbar or icons?

Came into work after being off Tuesday and the computer wasn't showing the taskbar or icons... I restarted it and same thing. Just logs on but doesn't bring up the taskbar or desktop icons. after some research I copied explorer.exe from a healthy computer and ran it on the malfunctioning one. My otehr problem is that I can't open folders either. I can access the Internet and other programs whn I hit ctrl-alt-del and run a new task. checked my registry and shell is set to run explorer.exe. I'm running a virus scan with Avast! Antivirus but not holding out much hope. Does anybody have any suggestions?