Hi, I recently bought the new model USB PC Light Gun from Act-Labs for use with MAME. For some strange reason I can't get it to work right. When I use the calibration switch to calibrate the gun, the bottom 2/3 of the screen turns dark grey, the top 1/3 turns white. When I switch back to normal mode the gun shoots all over the screen and is highly inaccurate. The calibration screen is suppose to go all white. It will only calibrate accurately within the white area.
But I can't get the whole screen to go white on calibration. In or out of MAME.
I have spoken with the Tech Support at Act Labs. They have given me several suggestions, nothing has worked. They assure me that my monitor and video card are compatible. I know the gun works because I hooked it up to a couple of friends systems and it worked fine. There is something wrong with my hardware/software setup.
I've tried everything in the troubleshooting section in the manual that was sent plus everything on-line. I switched resolution, interlacing on the graphics card, refresh rates, etc, etc.
I don't know what else to do!!
Has anyone else had a similar problem?
Any suggestions? Please help.

My system specs are:
Athlon XP 2600+
GeForce 4 Ti 4600; 128mgs Ram
21" Viewsonic G810 Graphics Series Monitor (CRT, VGA compatible)
768 Mgs DDR 333 Ram
Windows XP Professional
DirectX 9.0c
Thanks.