To put it simply, your computer is getting a bit old. I think you have a pentium D cpu in that, newer games a really going to stress it out. The powersupply makes no difference. Also, the amount of RAM you have is a little low. The only way you're really going to solve performance issues is with a new CPU, motherboard, RAM, and probably powersupply. The GPU you got isn't top of the line, but it should be able to run just about any game, some on low settings and resolution.