xserver problem - is there an alternative to re-install?

[R Kimber]

Having had a perfectly good 7.10 system, I bought a new mouse and
changed *ONLY* the mouse entry in xorg.conf.

Now, I can only boot in low graphics mode, and no amount of
re-configuration and re-booting seems to make any difference.  I have
tried reinstalling the nvidia driver, and using the nv driver, but all
I can get is 800x600, even though the xorg.conf file is the same as
before except for the mouse entry.

The new mouse seems to work fine (Logitech LX7).

I have amd64 x2, nvidia 7600GS, and all the latest updates.

Is there an alternative to re-installing everything?

- Richard.
-- 
Richard Kimber
http://www.psr.keele.ac.uk/