Windows XP Restart problem

I recently installed Norton Antivirus. When my computer restarted to
complete the installation, Windows never reloaded properly. It came up
to my desktop with my desktop background but no task bar. The only
thing I can do from this screen is ctl-alt-del to bring up Task
Manager. Several processes are running, but not explorer. There are no
applications running. If I try to start one I get a message that there
are no programs related to this extension and to go to control panel to
associate the file type. I can browse, but I can only see files when I
am viewing All File Types. If I am viewing only programs... it doesn't
recognise the exe files are programs.
I have the same results in safe mode. I can boot up to a command
prompt, but I can't figure out what to do after that. I have tried to
do a system repair. The System Repair window comes up, but it is blank
and I can't figure out what to do with it.

Any suggestions? I would appreciate any observations.
Thanks
Andrea