system won’t startup properly

I have w2k on a dell PIII-800 system, 256 MB RAM, 20 GB hd with lots of space. It starts up, goes to the login screen fine. Once you login, the wallpaper shows up, and the mouse pointer, but no desktop shortcuts or start bar. Ctr-alt-del work to bring up task manager, nothing looks amiss there. Same thing if I boot in safe mode. I can boot in safe mode w/msdos prompt and see a dos prompt. any ideas on what I can do to get back to a functioning os? Thanks!