Black screen upon exiting ns2, computer locks up

Hello everyone
I have been having this problem with ns2 on exiting the program
Whenever I exit ns2, the program will close and I will have a black screen and my Computer will completely lock up and I cannot get out of it, It won't even respond to the keyboard, num lock, caps lock, and scroll lock, wont even turn on or off
So then the only way I can get out if this problem, is if I hold down the power button on my computer and restart it manually
This problem has been driving me nuts and I might end up uninstalling NS2 for now until this problem is fixed

My Specs
AMD QUAD CORE 3.4 DENEB BLACK EDITION
HIS ATI 7850 1GB
12GB DDR3 RAM
500GB HD


My NS2 Settings
Everything on highest except Ambient Occlusion and Atmospherics turned off
1920x1080 Resolution