Windows > P4M800PRO-M motherboard won't start

Yesterday I went to help a couple of friends, trying to setup a new system for them. They bought a P4M800PRO-M (v1.0) motherboard with an Intel Celeron D processor and 512MB of 400MHz DDR. It is an impressive motherboard having a 1066 FSB.

Once I finished removing the previous hardware and adding the new one, I tried to turn on the system but... it wouldn't boot.

Explanation: Having read the manual thoroughly, I found there was a note concerning the power requirements for this mother board, which says:

Page 10
Connecting the 20/24-pin power cable
(...)However, using 20-pin power cable may cause the system to become unbootable or unstable because of insufficient electricity. A minimum power of 300W is recommended for a fully-configured system.

How to Fix it?: Make sure your power supply does have either a 24-pin cable or a 20-pin cable along with a 4-pin/12v power connector. Place them as explained in the manual on page 10. This should make your system boot.