Since the display shows while booting I'm going to share the usual fix without attempting to write a long step by step or any explainer.
1. Boot Windows in safe mode.
2. Change the resolution down to 800x600 and ok your way back to the desktop.
3. Click the Start, restart option and for most, that fixes it. Now you can in the regular boot mode change the video mode to support your monitor.
We have a Compaq with windows vista home premium, and a sony sdm-m81 monitor. The computer turns on fine, and shows the load status bar as the computer is loading fine, but when the computer turns on full, the screen is dark, the backlight is on and you can see the mouse arrow, and can move it. Same problem when you try to start it in safe mode. You can scroll through all the options on screen, but once you select one, again the screen is black with the backlight on and arrow visible.
We have been able to use this monitor in the past with the same computer. However, the resolution looked funny, and at times the positioning of the screen would be out of whack to the left, cutting off some of the icons.
Another thing to note is the fact that when I toggle between input one and two on the monitor, one says "cable disconnected" and is goes to sleep mode, while input two says no input, but remains on. Whadda think????