New ATI video card not being detected

Hello. First of al I am not really computer knowlegable so please excuse me if I might sound stupid  
I have a Gateway GT5228 destop with Win XP and want to install a video card because the nVidia 6150 built in one is kind of suxs. I bought a ATI Radeon HD 4670 1GB DDR3 video card. The instructions basically said stick the video card it and then install the drivers from the CD.
I opened the desktop found the PCI Express slot and stuck it in, started the comp and then installed the drives form the CD. I then unconnected teh monitor from my motherboard and tried connecting it to the VGA socket in the new graphic card. I got a black screen and my monitor has a [no signal found] on it. I tried restarting my computer and still see a black screen. When I pluged my monitor back into the motherboard socket, it works. I went to device manager and tried to find the video card and it s not showing up at all. I have met all the requirements for the video card to the best of my knowledge. It is has a core 2 duo processor with 2gigs ram, and a PCI express x16 slot. I changed the power supply to a 540w from a 300w so has the power supply.
So I am thinking for some reason its not being detected by the computer. I tried taking out the video card and reinserting it to make sure it is in there properly and it is. When I look at the video card from the side I see the fan on the video card spinning so it is getting power. I tried calling ATI and the person said it is a defective video card because when I restart the comp I should at least see the bios or opening screen. I am not sure if this is the reason. I bought it brand new and it came sealed in the originol box. I bought it from Newegg so its a respectable source but I dont understand how a brand new video card would be defeftive. Any ideas or suggestions would be very helpful. Thank you.