This forum comment seems to confirm this was because of a problem in the BIOS: http://ubuntuforums.org/showpost.php?p=1959501&postcount=76
-- Mouse pointer freezes in Dell Dimension E521 / nForce 430 https://launchpad.net/bugs/67734 -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
