Monitor not turning on with computer

I recently factory restored my computer, today actually. I had it running fine and was installing some of my old programs and transferring over some pictures I had put onto a flash drive. I left the computer on as I went out for 3 hours, allowing everything to finish and hope it'd be done by the time I got back. When I got back, the monitor was black and had a white stripe going across the middle with all weird colored dots within the white stripe. I figured the computer had frozen somehow, but now my monitor won't turn on at all. I manually restart the computer with the power button, I hear the fan going on and I even hear the beep noise, but my monitor is still black. When I touch the power button on my monitor, I get the noise it usually makes followed by the gateway logo. After a few seconds it just says no signal. What could be the issue here?