My father's girlfriend wanted to add a PCI modem to her computer. After installing the card, the monitor will not work. Normally, when the computer is off, the monitor will have a flashing green light and when the computer is on, the monitor light is solid. When the monitor cable is unplugged from the card, the monitor will say "The monitor is working properly, please check the cable. RED, GREEN, etc" When the cable is plugged into the card, the flashing "Monitor is working" goes away. Now the computer will boot up but the monitor stays black with the flashing green light. I've tried replacing the video card with no luck. Any suggestions?