Does the mobo have built-in video? If so, it may be using that as output, and not your video card. Some such systems need you to set the BIOS to use an add-in card. If that might be your case, try feeding the monitor from the mobo VGA output connector, not from the video card.
The other thing that can give you no performance is if you fail to connect the power cord from the PSU to the special 4-pin connector near the CPU. Some mobo's have this one is in addition to the main 20-pin power supply connector elsewhere.