I recently changed cases on my computer. It worked great after and before the change. It posted and displayed on screen, but now it is giving an error code 99 which is a problem with a PCIE card. So I changed out my 290 for another old HD6450 and an error code D6 came up which was "VGA could not be recognized". I have tried everything I can think of: clearing CMOS, changing PCIE slots. Can someone give me an idea of what to do?