New Power Supply, But Computer Won't Turn On

[caseythehost]

It's actually a little stranger than that. 

I got a new power supply and case today.  I thought my old power supply had died so I replaced it.  The new PSU works fine prior to installation in testing.  However, the PSU will not turn on once I connect the motherboard.  There is a very real chance the motherboard is dead since it is old, but I want to make sure I'm not missing anything here before getting a new one. 

There is no power getting to the motherboard at all, and once I disconnect the PSU from it, the PSU starts up just fine again.  Any ideas?

[patio]

Your front header jumper to the power switch on the front of the case is hooked up backwards...

[caseythehost]

I'll check it, but that doesn't make sense to me.  Nothing is connected to the power supply at all except the MB.  After I had problems I disconnected everything to use a process of elimination.  The PSU is only connected to the MB via the MB two connections.  The power supply itself will not even turn on now.  It has an LED display that turns on with no problem until I connect the 24 pin.

[dslgeek]

Read over your documentation for the motherboard.   
The motherboard turns on the power supply when you press the front panel button. It you pulled off the small wires that go to the front panel it will never turn on. 

[Aegis]

dslgeek is essentially correct, but he might better explain that the power button on the front of the computer completes the circuit.  The twenty-four pint "bus" from the power supply to the motherboard is what gets power to the central processing unit and motherboard, but it's engineered to be controlled by the push-in buttton switch on the front of the computer.  I kind of miss the old days when computers had large red "flip" type switches, usually in the back.  You knew that was serious!


dslgeek:  I noticed the "eye roll" at the end of your post.  It's nice to know you never make mistakes.

[caseythehost]

Ok, just so I'm clear on this. 

The power supply will turn on just fine until I connect it to the MB. 

After the power supply is connected to the MB the MB must be connected to the front power button on the case, and I can no longer turn on the power supply via its own switch.

Even though the power switch on the power supply is turned on, the LCD on the power supply itself still will no longer turn on simply because it is connected to the MB. 

If I disconnect the power supply from the MB, the power switch on the power supply will now power on the power supply.

I have never in all my years of building systems encountered a problem like this ... ever.  However, this is one of those new power supplies that doesn't use a fan so it's new to me. 

I just want to be clear that you all understand that the MB itself is preventing me from turning on the power supply via the power supplies own power switch.  How in the *censored* is the MB and case power button preventing a self-contained power supply from turning on?

[patio]

the power button on the front of the computer completes the circuit. 

[dslgeek]

I have been building home brew PCs for longer than I care to admit. 
I finally got it figured out. Sometime, a few years ago, they designed motherboards and PSUs so that the PSU will not go full power until the motherboard says things are OK. So that means to really test the PSU, you have to have at least an old motherboard that will pass the OK to the PSU. This is very scary. It allows  that the whole thing can be turned On or OFF by somebody on the other side of the planet! 
Just yesterday I had to have my daughter help me put the power switch wires back on the motherboard. I can not read the very tiny print they put on the motherboard next to the row of pins that have things like the lights, speaker and so on. And each board is just a little different. 

[caseythehost]

That is a little scary, but I'll give it a shot.  I just wanted to make sure everyone was understanding what I was trying to say.  Give me a day or two, and I'll get back with you all.  Thanks for the help everyone.