are u using a usb mouse?try plugging and unplugging for udevd to get mouse detected.another chance is wrong display size/driver set.may be u can show us ur /etc/X11/xorg.conf pasted in
http://pastebin.ca or similar sites and link here.also post ur monitor model display resltn etc
if gpm is enabled this may interfer with X too.
you may check the gnome menu preferences>mouse>Pointers for some options.
if everything fails,use swcursor option in Section device in /etc/X11/xorg.conf part.
Code:
Option "SWcursor" "yes"
or
Code:
Option "HWcursor" "off"
^ may that help after a gdm restart
you may need a display driver for nvidia either open source "nv" or proprietory 3d driver from nvidia!