There are many suggested ways of getting around problems in Excel - turning off Scroll Lock, pressing both mouse buttons simultaneously, clicking mouse scroll wheel, etc, etc, which sometimes solve the problem, but if not try a reinstall.
You could also post your question on a dedicated
Excel forum, see here.
A better option would be to download and install
OpenOffice 2009, the free office suite from Sun Microsystems. Its version of Excel opens and saves in all Microsoft file formats and works in a very similar manner. And it's less buggy!