Have you tried doing a factory memory recall first? The D9200 (and, I just found out, the 27" VP that was copied from it) have a history of memory corruption that can cause things like low brightness, no VGA image, etc. that can't be adjusted back to normal.
To get into the secret Factory Menu, hold the DOWN and SEL keys at the same time. When the menu pops up, SEL the RE (Memory Recall). Then try adjusting your picture again...