Complete System Freeze when log out of X session

[vangogh]

My laptop has xorg 7.3 on Freebsd 7.
My xorg.conf file has:
Section "Device"
    Identifier "card0"
    Driver "vesa"
    VendorName "S3 Inc"
    BoardName "VT8375 [ProSavage8 KM266/KL266]"
    BusID   "PCI:1:0:0"
EndSection

Problem is when I log out of gnome my system freezes completely and 
control+alt+backspace does not work. The keyboard becomes totally 
unresponsive and i must unplug the system to turn it off. I have 
searched this problem and seen that posts appear in the archives back in 
2006 about this issue. However, I cannot find any solution. Can someone 
please point me in the right direction for a solution to this please?