I thought you already solved the issue.
Did you reinstall the driver? What ASUS series and MSI card series you installed?
Since it became problem, I think you might have to do it one by one to rule it out.
There are many causes can be suspected such as the card getting defected, dirty slot, deficient power from PSU, incompatibility (rare), and some more.
Windows 8 do read any card installed but not always to its detail and use common simple driver available from MS. The memory size other than Intel based video card not always accurately detected. I find it happens when worked with ATI/AMD or Nvidia card. I did have problem with ATI in which after successful installation and restart the resolution suddenly drop to 800x600.
Windows 8 on my experience has issue with latest driver of ATI/AMD except we the latest ATI card.
Here the list I used to do in solving it:
Additionally you can follow this thread made by our senior member here
AMD Catalyst™ Drivers Windows® 8 Consumer Preview by
Righteous Dude
If your ASUS is Nvidia then try to do the the same way with different driver.
Hope that helps you a little
Kevin