No input signal on monitor

[masicno]

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. 

[matt]

Have you checked to make sure the new card is correctly installed (pushed in all the way and secure)?

Do you still get "No Input Signal" when you remove the new card and plug the cable into the original video card?  (Is the original integrated to the motherboard or separate and attached via PCI/AGP?)