As your system is a bit dated, you may be better off building a new one in the long run. But if you must stay with this rig to stay on budget, I would upgrade the video card to a 7750. I don't know what case this is in, so make sure it uses full height PCI slots in order to fit the new video card and has a PCIE slot. It's probably the onboard graphics that are causing your games to crash. For power supplies (again, I am assuming an ATX sized case), I would go with a lower wattage model from Seasonic. 450w should be enough for that rig and a new video card. You should list the name and model number of your PC so we can help you out more.