My friend has an HP Pavilion p6774y pc and I would like to help him upgrade the GPU and PSU. His price cap is around 300 bucks and Im just not sure what new components would be compatible with this pc. Any suggestions would be great! Thx!!
Depending on what kind of tasks he plans to do, GPU's can range anywhere from $30 to $1000. I'm currently using a $65 EVGA GT430, and it does everything I need it to do. I play Minecraft every once in a while and also use Photoshop/illustrator, and it's always just humming along. One step further would be the GT610, which my friend has, and also runs great. Both cards are compatible with your computer.
As for the PSU, any one will do. Just make sure they have the same connections. I'd recommend you a Corsair model.
Power Supply Internal 250W (100-240V) Form factor: internal ATX
Total Wattage: 250W
You need an ATX power supply. There are some really good ones and some really really bad ones and they cost about the same for some reason. Here is a good cheap one: Antec VP-450 - generally under $50. If you are buying a different one post over in the power supply forum. A bad power supply can give you un-debuggable intermittent software errors as the CPU and MB give the wrong answers back to SW.
At $300 minus $50 for the PSU you can get a monster of a video card which may have length issues and clearance issues. Paying less gets you a slower card that is shorter and does not game as well. In your price range look at HD7850. The best way to tell if it will fit is open the case and get out a tape measure. See what blocks the video card from running full length.