I also have a Dell C521 and opted for a ATI Radeon HD 4650. Fits fine but cannot get the card to display a picture. When I boot the PC with the card in, I get a message to switch to the videocard and I am kind of stuck in this loop. As I said the card fits but I cannot seem to get it to a picture
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Your motherboard have an integrated gpu, right? U must disable that before u can use your HD4650...