I've seen this before, try going to start->run and typing:

"C:\Program Files\Microsoft MapPoint\MapPoint.exe" /regserver

If you installed Mappoint to a nondefault location, change the location accordingly. But make sure the path is inside the quotes and the /regserver is outside.

-Jim Keller
http://jim.centerfuse.net/projects/
http://jimkeller.blogspot.com/