Hi when upgrading my friends computer, I got him an ultra 600w power supply which works fine. I also got him a radeon hd 7850, but it didn't work. I think it's due to the fact the it's a 3.0 card and the Mobo has a 1.0 pci express slot.
I also know that the slot works because I was able to run my old radeon hd 2600 pro in it. Since people say a 2.0 card should work (but not most 2.1 cards and I haven't had any info on 3.0s) I though about getting this: a 560 ti
It isn't necessarily because of the pci express slots a 3.0 card will work in a 2.0 slot but will only operate at a 2.0 level of performance.
You may want to go into the bios and see if the primary graphics adapter is set to onboard if so you may want to change it to pci-express now this can be a problem as a lot of store bought retail computers have locked bios which will limit what you can change or upgrade to.