This sounds like possible video card failure, but lets continue:
You said you have already disconnected and reconnected (our word for this: re-seating) the RAM and other hardware.
Is the video card a detachable card? Have you attempted to reseat this as well?
It might seem simple, but you might also check the connection on the back of the monitor itself. Often, the cable for the video or the power to the monitor might come loose.
Do other monitors work on this computer? If you have an extra monitor, it would be well worth the effort to see if the problem might be specific to the monitor rather than the computer/graphics card.
Let us know! Looking forward to hearing from you and assisting further if needed.