Dead New PSU?

[n925cu]

I have installed two new 400w PSUs to replace a 250w oem. Installing and connecting the cables is easy enough, but so far neither seem to be providing power. The LED on the MB does not light and the PC will not power up when I push the power button. What could be wrong? I doubt that two PSUs are duds.
The MB has a 24 pin main connection.

 

[luminaris]

Are you using a 925X board? They have two power connections. Provide some board specs and PSU specs. Just because a PSU says its 400 watts, that doesn't mean it actually puts out that kind of power. There are good ones and cheap ones.

 

[n925cu]

As near as I can tell, it is a 951 with two power connections. The 24 pin and a 4 pin.