Since you don't know your video card, I guess you are uncertain whether the driver is the latest. You need to find this out and make sure the driver is current. Check your cable connections to the card and monitors. Check that the system knows your monitors by exact make and model. If not, go to the manufacturers web site and get proper drivers for these as well. Once this is done, check your resolution and refresh rates. Setting either or both of these to higher limits might decrease color resolution which could explain the drop you are experiencing. Good luck.