I bought a ATI Radeon HD 4670 about a week and a half ago and it has been working perfect till yesterday. Well, the other day while I was on my computer the power cord fell out of the wall somehow and my computer shut off. When I plugged it back in and turned it on I got to my desktop and everything seemed fine until I went to start up a game and it told me it couldn't detect a suitable display device.
I went to device manager to see what was listed under display adapters to see my onboard there and my radeon not there. So I right clicked and disabled my onboard and everything was still working fine...with no display adapters.
After that I restarted my computer to see if it would detect it on start up and I noticed that my disk drive was making a weird noise, kinda like it's trying to start up but my disk drive works fine. Well when it started up and I got to my desktop, there were still no display adapters listed. I ended up turning off my computer than opening it and making sure the graphics card was seated correctly and it was. I unplugged the power to my disk drive then closed everything and started it up and there was no weird noises. But it took longer than usual to get to the splash screen. I should also note that the fan on my graphics card is working fine so it is getting power.
If I could get some help with this it would be nice, because I'm out of ideas and I am planning to RMA the card if I can't get it fixed somehow.
As "Maziar" said, sounds like your driver got corrupted somehow. You could go to ATI's website and redownload the specific driver for your card. Do you have a disc that came with your card. It will have the right driver on it. Good luck.
Before you RMA your card, uninstall all you video drivers and shutdown.
Boot up and double check your bios and make sure that your onboard video isn't turned on.
From your post you said that you seen your onboard vga listed in your device manager. If it's trned on in your bios, there's your conflit.
"RMA stands for Return Merchandise Authorization. Basically when you RMA something, you send it back to the manufacturer or an authorized service shop, and they send you some form of replacement."