Explorer unable to load during startup

After restarting another computer in my house windows xp can no longer load explorer.exe, and only the wallpaper shows. I can access and use all the programs with the task manager, only windows explorer wont load.

Ive tried using system restore but it can't seem to load. (same result when i try it in safe mode)

Scanned with adaware, used virus scan, nothing seems to get it back to normal. Does anyone know a fix for this problem other than reformating completely?