Just wonder if anyone's ever had this happen.
My monitor just goes black. When I start up the computer, I can see the post, then it goes black,
you sure that u have not just a glossy display mirroring?

I think your electrolytic capacitors of monitor powersupply are dead/dieing. Its getting colder now and they have more hard time to reach enough capacity. You could try to heat the room up or the monitor or at the capacitor os the power supply area if they have "coneheads" and replace them by new ones.