Mouse and Keyboard not detected

I just finished putting together my new Asus A8n-SLI motherboard, and everything else.
When I started up, it won't detect my USB logitech mouse or my normal keyboard, The keyboard light will go on, but no matter what button I press, it won't have a response, and my USB mouse isn't detected, or gettnig any power, because it's not even turning on(The Laser isn't turning on when the PC start, like normally)

Everything else is plugged in, and I redid the wiring too, but this problem still persist.
The only thing I haven't tried is to try a new power supply, because the board require a 24-pin, but I'm only using a 20-pin, and the extra 4 hole, I placed into the hole to the upper left corner in the motherboard the 4pin12Volt, as recommended by someone else.

What would cause my keyboard and USB mouse to be not detected, could it be the 20-pin PSU, so do I need to find and buy a 20-pin to 24-pin converter or get a new PSU, since the rear connector(Keyboard, mouse, USB hole, don't seem to be getting any power)

My current PSU is a 400 watt Antec SL 400

 

I dont think your usb mouse will be reconized till you get into windows, are you just getting to the post screen? If you are, your keyboard should work. Have you tried another? ed

 

Sorry, missed the part where you are not using the 24 pin psu. . ed