Sounds like there may be pieces of the WAMP Install left over that are conflicting with the XAMPP server.
Did you stop the WAMP Services before uninstalling it?
there may be left over widows services from the WAMP install that are trying to run at the same time as the XAMPP services.
did you try creating a php page in the XAMP htdocs folder and accessing that to test the servers basic functionality?