Unplug the mouse and boot up (odd thing you'll run into, easy to fix.)
Try SAFE MODE (varies with Windows version so google that.) Report what happens. DO NOT SKIP THE MOUSE TEST I NOTED FIRST.
After turning my Dell Inspiron 531 off for a week, it now says "Auto Detect, Entering Power Save" when I turn it on. I tried taking out the battery and resetting date/time, but nothing changed. The green bar above "Microsoft Corporation" runs prior to seeing only a black screen with the white cursor. All monitor functions seem to be fine. Any thoughts?