|Why did you change the PS ?|
If you were having problems, what were your symptoms ?
If you're changing it because you think it failed, if it DID fail, sometimes a PS damages something else while failiing, most often the mboard itself, and in that case replacing the PS doesn't fix the problem.
Replacing it with one that has less wattage capacity may not allow the mboard to boot if one or more graphics card(s) is (are) installed in (a) mboard slot(s).
If the PS has a switch, make sure it's in the ON position (the side with the line symbol closest to the case).
Did you plug both (or all three) of the necessary power connectors into the mboard ?
Your asus p5n-d mboard has both a 24 pin main power socket and a 4 pin power socket. You must connect both a 24 pin and 4 pin connector from the power supply to the mboard.
The 24 pin connector on most recent PSs wiring is in two pieces - a 20 pin and a 4 pin connector coming from the same wiring bundle - the 4 pin part attaches to the 20 pin part - you must fill the 24 pin socket on the mboard with those.
The 4 pin power socket is elsewhere.
Some PSs have an 8 pin connector that is two 4 pin pieces from the same wiring bundle that may or may not be attached to each other, rather than just a 4 pin one - one of those two 4 pin pieces fits in the 4 pin socket.
The shapes of the plastic surrounding the pins on the connectors from the power supply and in the sockets are designed such that you can't plug them into the wrong socket or backwards.
If you have (a) graphics card(s) installed in (a) mboard slot(s)....
- if the graphics card(s) has (have) one or two power sockets on it (them) , you must plug connectors from the power supply's wiring into that or those sockets such that they fill the sockets. Most cards that have power sockets have 6 pin sockets - use a 6 pin PCI-E connector - some have 8 pin sockets - use an 8 pin PCI-E connector, or a 6+2 Power connector (a 6 pin and 2 pin connector on the same wiring bundle that can usually attach to each other).
- if you don't have enough PCI-E 6 pin or 8 pin ot 6+2 pin connectors for the number of sockets on the card(s), DO NOT use a PCI-E Y cable - one female connector to two male connectors - that can't supply enough current. Use a proper wiring adapter - e.g. two larger molex (male pins) connectors to one PCI-E 6 pin (male) connector in the sockets you don't have enough connectors of from the PS.
- Your power supply must have at least the minimum capacity required to support a system with the graphics card you are using installed, or the max graphics card you might install in the future.
(Onboard video - video built into the mboard - IS NOT A CARD ! )
If that info is not in the ad for the video card, you can go to the video card maker's web site and look up the specs for the model - often under system requirements - the minimum PS wattage, and, more important, the minimum amperage the PS must supply at 12v is stated. If you don't find that, any card with the same video chipset including any letters after the model number has very similar minimum PS requirements. Some power supplies have two or more +12v ratings - in that case, add those ratings to determine the total +12v current capacity.
If you're a gamer...
In most if not all cases, the max capacity rating of the PS is an intermittent rating. It's recommended that you do not load your PS to any more that 80% of that rating if you are going to be using something that puts a constant load on it, such as playing a recent game for hours on end. In that case, you multiply the min capacity stated for the system with the particular video chipset on the card by 1.25 to find the min. capacity of the PS you should have.
If you need to get a PS with more capacity, you can usually replace it with any decent quality standard sized standard ATX PS.