Could be the monitor settings don't match the video output or the video card has failed. Try entering the BIOS setup screen at startup. Usually the 'DEL' key held down. If screen is displayed (It will be in default VGA mode at that point), then you know the video stream is OK. Continue booting, and press F8 to enter windows safe mode, and continue from there to get the display parameters corrected.
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Could be the monitor settings don't match the video output or the video card has failed. Try entering the BIOS setup screen at startup. Usually the 'DEL' key held down. If screen is displayed (It will be in default VGA mode at that point), then you know the video stream is OK. Continue booting, and press F8 to enter windows safe mode, and continue from there to get the display parameters corrected.