My monitor flickered to the point of going dark. I reset the resolution, and it was better for awhie. Then it started flickering again. I reset the resolution again, but it has started to flicker again, and is very dim. It is an emachine with a very old monitor.

Is this an LCD monitor? It sounds like the inverter or backlight bulb (or both) are failing. But to be sure, you need to swap that monitor with another computer. If Monitor 2 flickers on your computer, the problem is in your computer. If the problem moves to computer 2 with your monitor, you know it is your monitor.