I have a Dell 17-inch E173FP flat panel display monitor. Just after I visited a website, I left the room and returned to find that the monitor had gone black and that the on/off light was flashing every few seconds. Unplugged the monitor from the outlet, plugged it back in, but no change. Couldn't shut down my computer as a result and so I just had to turn it off manually. Any idea what's wrong with the monitor?