I had a fully working computer set up with a Corsair CX600M PSU, and a Radeon HD 5450 GPU, but I needed a more powerful GPU, so I bought a Gigabyte R9 280x, (This one: http://www.gigabyte.com/products/product-page.aspx?pid=5266#ov), and put it in, but when I turn the computer on, the GPU produces no output to the DVI or HDMI, but the fans turn. When I press the off button, the computer immediately turns off, so it probably didn't boot into Windows either. I've got the Catalyst 13.1 drivers installed, and I installed the drivers supplied in the DVD. I bought the card on ebay as new from the box, and the listing has now been removed. The motherboard is a Medion MD-7***, and the GPU is in a PCI-E 2.0 x16 slot. When I put the old GPU back in, it works fine.
UPDATE: I got a replacement from the seller, it doesn't work either.