Do you have the card seated properly? I thought I had my 8800 gts pushed in all the way. I boot up the computer and get no video on the monitor, but I don't remember if it was beeping or not.
Look at the slot. Can you see any of the metal exposed between the card and the slot? if so, its not pushed in all the way. I thought mine was pushed in, then looked at it, and lo and behold, it wasn't! I then pushed it in and it worked fine.
According the the manual you are experiencing either a DRAM error (continuous long beeps) or a power error (continuous short beeps), so either re-seat the ram or check all power connectors. I doubt the power supply is the problem because the system boots up with the older card, and it looks like the PSU would be able to handle your system.
I had the same problem with a new 8800GTS plugged into an asus P5B mobo.
However pluggin in the gfx card power hasn't helped - the pc turns on, the HD runs, the fans run, there's no beeps but it shuts down after about 2 seconds, then starts up again, and stays up.
However there's no output on the gfx card - I just get a blank screen.
I've tried reseating the card, checked all the connectors but nothing.
I suspect that the card is dead, but it could also be a dead mobo or the psu is not up to the job (450W)
What's the best way for me to determine what's causing the problem, given that I don't have another pc to try the new components in?