Question : Problem: ATX vs. ATX Micro Motherboards

I just replaced an Asus motherboard in a ATX case and power supply. The new motherboard is an Asus P5KPL-CM.  My old motherboard only had 20 pins on the main power connector.

This new motherboard has a 24 pin connector.  When I plug in the power supply connector, the last pins, 21-24 are vacant.

I cannot power up the new motherboard.  I think it is because my power supply has to have a 24 pin plug.  I just want to make sure that is the case before I buy a new power supply.

Is this the reason I cannot power up?

Answer : Problem: ATX vs. ATX Micro Motherboards

Yep.  A few motherboards don't require all the pins, but most do.