PC upgrade specs question.

[Tanker]

What games do you wish to play Fubar?

The pc you have sounds like it will work well on anything except high settings on the newest FPS or a game like World in Conflict.

If you want a new one, look at getting a bare bones system with the case, power supply, mother board and hard drive installed. That way there is no compatability issues and if it's all from the same vendor they can't say any issues are the fault of other components.
The bare bones will turn on and you'll be able to use it.
Then you can install the vid and sound cards, optical drives, more hard drives, etc of your choice.