Booting Trouble

Hello any and everyone. I just installed new a motherboard and new memory module to my computer and nothing is coming on the screen, nothing at all. I remove the memory and and get beeps but when I replace it nothing happens.

There are no PCI cards in it so those won't be the problem.

I remove the heatsink from the processor, turn on the computer and the processor heats up, still nothing on the screen.

I notice though that the fan that is connected to the power supply spins slower that it should, could it be the power supply that is the problem? though I doubt. It's a 450W power supply.

Any diagnosis suggested would be greatly appreciated