Blank screen after graphic card upgrade

Hi!

Recently, my graphics card ”Geforce 7900 GTX” PCI-e 1.0 started having problems with 3D programs, it is working fine with 2D programs. So I thought it was time to upgrade. My motherboard has a PCI Express x16 1.0 slot. I checked out the net and it seems that graphic cards with PCI-e 1.0 are almost extinct. I did a small lookup and found that PCI-e 2.0 graphic cards are supported by motherboards with 1.0 slots.

So I bought a new graphics card, “ASUS Geforce ENGTS250 Dark Knight” PCI-e 2.0. I’ve done graphic card upgrades before so I know the procedure (uninstalling older display drivers first and so on). When I inserted the card in the 1.0 slot and connected the extended power supply (the same that was used by 7900 GTX) and started the computer, all I got was a blank screen. The cooling fan turns on and runs for some seconds and then turns off. On other restarts it continues to run.

I also tried starting without connecting the extended power supply for the graphics card. What i got was a continuous beep from the computer. I don't know what that beep means in terms of POST error. Maybe someone can clarify. What is interesting here is that i don't get this beep when i start the computer with 7900 GTX without power supply.

When I re-inserted the old 7900 GTX, it worked fine.

I read on the back of the box for the ASUS ENGTS250 that it requires a minimum 450 W system power supply (with 12 V current rating of 24 A). After reading this, I checked the specification of my PSU. This is what I found:

Delta Electronics , INC
Model: DPS-460DB A
Input 100-240V ~/8A
Output +5V /13A
+12Va/16A +3.3V/17A
+12Vb/15A -12V/0.8A
+12Vc/8A +5Vstb/2A
Max Power: 460 W
MAX.Combined POWER ON +12Va, +12Vb,+12Vc EQUAL TO 385 W

After reading this I get the feeling that it’s my PSU that is the issue here, but I am not so sure. Specially because I have inserted a PCI-e 2.0 card in a PCI-e 1.0 slot.
I need someone’s opinion someone, who has had a similar experience. Please Help!
Here is some more info on my hardware:

The computer is a HP d4580.se.a, check out the link

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00...

The motherboard is a MS-7225 (NASH), check out the link below for more details:

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00...

If simple clicking doesn’t work, please try copying the link.

Thanks in advance!

Regards,
Sanchit