I'm thinking of buying another PC anyway. But this system has lasted me 7 years - I recently upgraded the memory so if I replace the CPU and motherboard I'm hoping my mother will get another 7 years out of it.
google the numbers on your motherboard and see what comes up or search it on ebay. Don't be surprized if its the power supply though. It is doubtful that the processor and the board are both bad its one or the other most likely.