I understand that you are experiencing problems with the recognition of your video card on the Intel(R) Desktop Board DZ77SL-50K.
You may be experiencing a BIOS corruption that we can try to fix.
I recommend you to boot the system in to maintenance mode, press F9 to load BIOS defaults and then press F10 to save and exit.
Boot the system in normal mode and get in BIOS, in the boot tab you will have an option called expansion card text, enable this option and press F10 to save an exit.
Turn off the system and move the monitor cables to the video card and turn the system on.
If problem continues try doing a BIOS recovery. You can find the instructions at the following web site: