It's your graphics. Absolutely. What do you have for a video card? Or if it an "on-board" video (on the motherboard) like an Intel Video chip set. you will have to replace it.
Things you can try...
1) download the latest video drivers.
2) right click on the desktop, Properties, Settings(tab), Advanced, Troubleshoot and change the Performance slider down, one notch at a time, and try Mastercam again.
3) Replace the video with an Nvidia Card/Chipset.
I use the FX 5200, FX 5700, FX5900, and the all work great. These are the bottom end cards now days. They can ce had for as little as $40. Better card = better performance. Get as much memory as you can afford. Miinhave 128MB & 256 MB
Mike Mattera
Tips For Manufacturing Training CD's, DVD's for Mastercam, SolidWorks, Inventor, G-Code Training & More
http://www.tipsforcadcam.com