Autocad images preview but appear all black on loading

Hi

I'm running the Jan 2012 version on W7x64 and when I go to load an existing Autocad file I 'see' it in Preview but when I load it the workspace appears totally black.

I suspect this is some type of video driver problem. My W7x64 has a 'normal' AMD dual head graphics display - nothing special.

Any thoughts pls?

Thanks

David