Graphics issue.
You might try powering down, disconnecting the video card, power up then down again after a few seconds, then put the card back in, connect the monitor and power up. This will not make one iota of difference if it's a driver issue, but might help if it's a messed up hardware issue. I've seen the same method of removal, powering up/down then readding, sort out hard drives that couldn't be seen or wouldn't boot.
As the old cliche says, "it's a long shot, but it might just work".
