This is a stock gateway computer gt5228, with on-board video card, I was using it and left for about 1hour and when I came back the screen was black like the power saver or screen saver had kicked in, so I moved the mouse to wake it up but nothing happen, so I turned it off and unplugged it from the power, and tryed to restart the tower lights up and makes a noise like it starting, I did not remember hearing any beep when starting, there is a light on the power button on the screen so it getting power, and a box comes up that said No signal , keyboard dose not light up, I have not change anything, what could be some things that may have happen, or what could I try to maybe get it working, thanks for any Help.