Mouse not working with xorg

I installed debian sarge, upgraded to etch, installed xorg and gnome and had them running fine, then when I rebooted the computer gdm wouldn't start. It kept saying it couldn't find the mouse.

I ran mdetect and it did nothing. Then I ran mdetect -v and it said it found /dev/ttyS0, so I changed the xserver configuration from /dev/input/mice to /dev/ttyS0. Now gdm is working, but the mouse doesn't move.

It's a USB mouse with a PS/2 adapter on it, and it plugs into the normal PS/2 mouse port in the back of the computer.

Where am I going wrong? If you need more information I'll post it right away.

Are you using a 2.6 kernel? If so, then the mouse device should be /dev/input/mice. Maybe you need to run "dpkg-reconfigure xserver-xorg" to reconfigure your X settings.