Required reboot doesn’t work.

I just got a system that an end user obviously upgraded to 2000 Pro. Have no clue what he did along the way. I’ve restarted many times and it does not work. When I try to install Windows Updates I get the following error message.
“A PREVIOUS INSTALLATION HAS PENDING WORK REQUIRING A REBOOT. YOU NEED TO RESTART YOUR COMPUTER TO COMPLETE THAT INSTALLATION BEFORE RUNNING INTERNET EXPLORER SETUP. SETUP WILL NOW CLOSE”.

I also get a very similiar message when trying to load SBCYAHOO dail up software.