Blackout

Does the video card have a cooling fan on it or a passive heatsink? If it has a fan then make sure it is working when the computer is on. If it does not have a fan you could try installing a small fan on the heatsink to help cool it. Is your powersupply rated high enough to work on that video card? High end video cards are very power hungry and might be taxing your current power supply. If the voltage drops it could cause the video card display to shut off...especially when playing video games at high res. Verify that the video card is properly seated into the slot and you may also want to try and remove the card, clean the contacts, and the re-insert the card. And if you are using software to overclock the card or if you computer multiplier/FSB has been raised then this can raise the clock speed of the agp/pci-express port and cause video problems. Also verify that the agp/pci-express voltage is adjusted to what the video card requires.