Start menu missing

Hi guys, i have a problem with my dell notebook...i have been reading this blog it is a quite similar problem..my desktop icons and start menu have completely gone but some programs i can run through task manager but the problem is that i can't find explorer.exe when i do it through run from task manager it says 'cannot find...' so i don't know how i can restore it back ...i have windows xp. IF SOMEONE CAN PLEASE HELP!!! thanks