After installing the ATI Radeon HD 5670 video card in a HP DX2200 : PCIe x16 slot, the computer (which has a 650W PSU) won't show video and won't POST. It just hangs. Hard drive clicks. Hard drive activity light on the front panel blinks frantically. Stays that way till PC is manually powered off. PC works fine if card is removed.
Any ideas on how to make this card work?