you don't need to purchase news parts to test all components.
first of all start by disconnecting hard drives, cd drives, memory, cpu from the motherboard and started from a blank motherboard with only the power connected to it.
Turn the PC on, you'll probably get no display but make note of the beeps.
then plug in the CPU and try again.
then the memory - if you have multiple modules try one at a time.
add the hard drive and see what happens.