I have a Compaq Presario S-series computer with Pentium 4 and Windows XP. When I go to turn it on, nothing happens on the screen. I have a new video card that is set to send the signals to the monitor but I have my monitor set to have a white box that says 'No Input Signal' whenever there is none and I don't get anything on the monitor but that box. Would anyone know what I should do? I've also tried plugging the monitor into the original slot that came with the CPU.