[Zutant]

Got a friend who has a HP Pavilion 061 we bought an antec 430w power supply installed it and when we hit the power button we geta 1/2 second hit of power and then nothing untill we unplug the cord and try again.

We tried with nothing connected and got the same results.
When we completely disconnected the psu from the motherboard and jumped the power on pins it starts.
We put his old psu in and the computer powers up.

 

[daddyhominum]

How many pins on the PSU and how many on the MB?
Did you buy a 24 pin connector for a 20 pin MB?

 

[jackdw]

A 24 pin PSU came with a case I got. I didn't realise that 4 of them were removable. Check for that.

 

[Frank4d]

We put his old psu in and the computer powers up.

I think you got a bad Antec power supply.

 

[JohnWill]

Sounds like the MB isn't seeing the PG (Power Good) signal.

 

[Zutant]

I think you got a bad Antec power supply.

Powers up when we jump the power pin on the connector.

24 pin psu and board.. unfortunatly I'm helping him over the phone since we live 1700 mile away so he may have connected someting wrong but from what he described it sounds right

 

[JohnWill]

When the MB controls the power up sequence, it insists on the proper voltages being present. When you jumper the P/S pin directly, it will power up, but that doesn't mean the MB is seeing good power.

 

[DeLorean]

If you have a multimeter you can test the supplies coming out of the PSU.

http://www.playtool.com/pages/psuconnectors/connectors.html

Halfway down this page there's a pin layout for the 24 pin connector.

This way you can see if the PSU will satisfy your motherboard, as JohnWill mentioned.

PS. I assume anyone who owns a multimeter knows exactly where not to stick it's probes, if not don't attempt this