Xubuntu mouse cursor disappears

[raydar]

Hi. I am using xubuntu 11.10 on 2 similar spec pcs. 512MB ram, pentium 3,but one has nVidia NV5M64 and one has intel graphics chipset. i use openbox with lightDM and XFCE4-panel. the pc with intel graphics is fine,but on the pc with nVidia what happens is my mouse cursor disappears totally at random. the pc hasn't crashed, and I can still do anything by keyboard,but the only way I can get my mouse cursor back is to reboot. Does anyone have any ideas. Thanks, Paul.