Asus P5N32 Which is quite old tech as it is a socket 775 motherboard and we must be about 3 or 4 generations further on. But that is not to say we cannot find you an upgrade or two.
Can you take of the side of the PC and post the wattage of your power supply unit? It will be on a label. Also how much memory have you got/
It would be useful to know how much of a budget you have? As it is very difficult to advise without knowing how much we have to spend.