I have a customer who runs a Dell tower (not sure of the model...I think it's an Optiplex). She was having trouble with her display (wouldn't stay on). So I had her change monitors. That seemed to fix the problem, but now she's still having the same old trouble. She can turn the monitor off and back on, and the image will appear fine for about 3 or 4 seconds, then goes black. The power button on the monitor remains green however. I thought it was the video card, but then why would the problem go away temporarily when the monitor was changed? Any ideas?