Maybe it has something to do with this issue?
http://en.wikipedia.org/wiki/GeForce_8_Series#8800_GT"Compatibility issue with PCI-E 1.0a
Shortly after the release, an incompatibility issue with older PCI Express 1.0a motherboards was unmasked. When using the PCI Express 2.0 compliant 8800 GT or 8800 GTS 512 in some motherboards with PCI Express 1.0a slots, the card would not produce any display image, but the computer would often boot (with the fan on the video card spinning at a constant 100%). The incompatibility is mostly with motherboards with VIA PCI-E 1.0a chipsets.[citation needed]
Some graphics cards had a workaround, which was to re-flash the graphics card's BIOS with an older GEN1 BIOS. .... [But] flashing of the video card BIOS voided the warranties of most video card manufacturers (if not all) thus making it a less-than-optimum way of getting the card to work properly. A workaround to this is to flash the BIOS of the motherboard to the latest version, which depending on the manufacturer of the motherboard, may contain a fix. In relation to this compatibility issue, the high numbers of cards reported as DOA (as much as 13-15%) were believed to be inaccurate. When it was revealed that the G92 8800 GT and 8800 GTS 512MB were going to be designed with PCI Express 2.0 connections, NVIDIA claimed that all cards would have full backwards-compatibility, but failed to mention that this was only true for PCI Express 1.1 motherboards. The source for the BIOS-flash did not come from NVIDIA or any of their partners, but rather ASRock, a mainboard producer, who mentioned the fix in one of their motherboard FAQs. ASUSTek, sells the 8800 GT with their sticker, posted a newer version of their 8800 GT BIOS on their website, but did not mention that it fixed this issue. EVGA also posted a new bios to fix this issue.[20]"