Question : Problem: PC won't POST after install of new Geforce 8800 GT

System:
Abit I-95 motherboard w VIA chipset & PCI-E x16
2048 Mb DDR2 533
Pentium D 940 @ 3.20 ghz
180 gb Maxtor IDE HD
250gb WD SATA HD
Lite On DVD 20x
CoolMaster Extreme Power 550w PSU = 12v1- 16 A 12v2 - 16 A  w/1 PCI-E 6 pin cable
Soundblaster Extreme soundcard
EVGA Geforce 7600 GS - upgrading to PNY Geforce 8800GT
Vista Ultimate

Although this is not intended as a gaming rig I recently purchased a Geforce 8800Gt to upgrade graphics for Photoshop. Prior to install I replaced the PSU to surpass the card requirement of at least 400 W and 12v -26A. Also updated to Via's latest 4 in 1 chipset drivers for mobo. Onboard VGA has been disabled. System runs well and stable with existing geforce 7600GS. Replaced the 7600 with a new PNY Geforce 8800 GT 512. Attached 6-pin power cable directly to graphics card for PSU.
The PC will not POST at power on. No beeps from the case, nothing on the monitor. Power comes on, case fans, CPU fans and video card fan come on , keyboard lights up and then it begins to loop, never getting past this stage. I have reseated the card, changed the DVI cable,verified the power, removed power from all but 1 HDD and 2 fans, & reset CMOS. Same result, no POST. Removed the 8800 and replaced with the old 7600 and PC booted as normal with no issues. Not getting much help from PNY/Abit. I can't tell if this is a compatibility issue or  possibly a bad card out of the box. Trying not to spend the next month doing RMA with PNY to find out it's another issue altogether. Anyone have ideas as to what else I can test or heard of a similar experience with the no POST? The only other ATX PC I have access to is identical to this system and results are the same.

Answer : Problem: PC won't POST after install of new Geforce 8800 GT

Your power supply is fine.   Dual 16A rails are plenty of 12v power ... and the PCI-E auxiliary plug will be on a different rail than the primary ATX connection, so the card has plenty of available power.

The most telling statement in your question is this:   "... The only other ATX PC I have access to is identical to this system and results are the same. " ==>   Identical PC, same results ... so you either have a compatibility issue or simply a defective card.

... I scanned a couple of forums; and it seems the G92 GPU used in the 8800GT has a compatibility problem with Via chipsets.   I suspect this is your problem (although user forums aren't always the most reliable source of technical info).   Your experience certainly tends to confirm this.   If it's not a budget-buster for you, the 8800GTX does not use the G92, and (according to the forum posts) works fine with Via chipset boards.
Alternatively, you could buy a Radeon 3870 which should give you close to the same level of performance without any compatibility issues [http://www.newegg.com/Product/Product.aspx?Item=N82E16814102719 ]