PSU works for Biostar and doesn't for ASUS

[gev]

My PSU is 450 W (24 pin). It has worked for my Chintech VNF4 mboard, it worked and woks for Biostar TA790GX 128M , however it doesn't  for ASUS M4A785-M.
I remove all components (RAM, HDD, Vcard...), leave just mboard and CPU (Biostar works with the same CPU pretty good) and when I start it, it works for 1.5-2 seconds and stops. The next time it starts is only after I remove the power cord, wait for about 3-4 seconds until the led on the board is off and plug it back in, but again with the same outcome.
Please advice.

[JJ 3000]

Do other PSUs work with that board?

It could be a bad mobo.

Is the board mounted in a case?

Are there any other peripherals plugged into that board?

[gev]

At least one other PSU worked.
Biostar that works is mounted in case, but ASUS no. I plased it on a non-conductive bench and then tested.
No peripherals plugged in, except for CPU (which as I told before works OK with Biostar).

[Geek-9pm]

Some moder Motherboards will not ork without a grounp plane. The need to have a metal tray or sheet  underneath. With spacers, of course. Moust the board as indicated in the instruction manual. The manual does not say you can test it without a metal plane under the board.
That fact that it often works anyway does not mean that is the way they want you to use it. The metal case is part of the design paameters.

[gev]

Sorry, couldn't quite understand what exactly you mean. However, if you mean to say that in some cases the metal case provides "Ground" contact, we can exclude this too, since at first I tested it monted in the case. Then when the problem was seen, I removed it from the case and tryed out of it.

[gev]

Besides, as I told before, it works using another PSU. Also the PSU it doesn't work with, works OK for another mobo (Biostar). Mistery huh:)

[Geek-9pm]

OK. I could not think of the right terminology. It is a 'back plane' that provides a reflective shield for VHF signals. Without it the system can become unstable.

The symptoms are typical PSU shutdown from thermal overload. The mother is making your PSU run hot. You can use a bigger PSU, but that  just ignores why the mother is drawing so much power.

http://support.asus.com/PowerSupplyCalculator/PowerSupplyCalculator_right.aspx

[gev]

I doubt that this can be the rason either, cause after the start, it works literally 2 seconds, no more. For sure this doesn't give enough time for PSU become overheated. By the way that other PSU that works OK for this mobo, provides even less power than this one does. The one it stalls with is 450W, the one it works OK with is 400W. I don't think ASUS power supply calculation makes sense at this point, since as I told, now I removed all peripherals, except for CPU.

[gev]

Looks like the issue is resolved. I was just told that there are a couple of burnt condensers in the PSU. For some reason although it didn't affect the Biostar, it did affect ASUS. Those condensers are replased now. I'll check that out later on.