SW Background changing to black

I did a search and did find some information about this butdid not really find out what solved the problem.

I am having the problem that after working awhile in SolidWorks,things like lighting, backgrounds, and shadows start to not workright. At the same time I notice that the background for SW(normally gray with the DS SolidWorks) changes to black.

Some comments suggested that it is a thermal problem but no realdefinitive answer. As I work in a very cold office, I don't thinkit is a thermal issue but I can take the cover off the computer andmake sure that it is clean and fans are working, if I need to.

One of the reasons I am posting this is that all of the commentsbefore were about SW2008. For me this just started happening when Iwent to SW2009 (currently at SP1). I have done all of the things myVAR suggested short of buying a new display card.

Any suggesting or better yet, someone that had the problem andsolved it, tell me what you did.

Thanks,
SolidworksGeneral