New memory and CPU

I installed a new AMD Duron 1300MHz CPU and RAM into a new motherboard. While the fans and hard drive operated when I powered up, the computer didn’t boot and the monitor remained on standby. I tried a CPU and RAM from an operational unit, and the computer booted up several times. Then it displayed the same symptoms as the new CPU and RAM. I then put the CPU and RAM back in the previously operational computer, but that now won’t boot. Does this sound like a CPU problem or could it be just RAM? Any other suggestions?