Mouse pointer change
 

I'm running Excell 2003 on Windows XP pro. Everything is set
completely normal and standard. Suddenly the mouse pointer in Excel
(only - no other software as far as I can see) has changed to a big
black square. It still seems to function normally but you cannot see
where it is pointing of course. It only happens in the cells area -
outside in menus etc it changes back to a normal arrow etc.

Done the usual switch off switch on, look at mouse pointer settings etc
and can find nothing odd. Only thing I have had happen which is out of
the ordinary is that pdf file thumbnail view decided it didn't want to
work - can there be a link?!

I found a fix for what looked like a similar problem on this site from
1998 but it didn't fix mine. Anyone any ideas?