so what windows is doing is disabling aero to improve performance .this can happen when old or buggy programs are run or if you have an underpowered system that cannot handle win7. youre system should handle aero without a problem.
what is aero = (http://windows.microsoft.com/en-US/windows7/products/features/aero)
you should go to http://www.hisdigital.com/us/download.shtml
and down load the latest drivers.
2 Type "sysdm.cpl" (without quotes) Press Enter
3 This will open your "Performance Options" click the "Advanced" tab.
4 Under the "Visual Effects" tab click on of the radials other than the default which is let windows decide and that setting will stay.