What Do you think can be the cause

[D_block]

the Pc behaves like the power supply is dead , no response when the on off switched is pressed . when it was replaced with a brand new one the same thing occurs . when you remove the P4 connector from on the board and press the power button everything lights up ( system doesnt boot )

ive seen this for the 3 rd time dis yr , once on an AMD unit an Twice on Intel machines , what can be the cause of this problem ?

im thinking it may be associated with the mother board , what do you guys think ?

[ripken204]

do you have a speaker hooked up to it to hear for diagnostic sounds?

what sounds do you get when you remove the ram?

[puntoMX]

...when you remove the P4 connector from on the board and press the power button everything lights up ( system doesnt boot )

I´ll put my money on the motherboard; a defective CPU is less likely but could be the problem too.

[ripken204]

a defective motherboard is also my guess right now as well, hopefully he has a pc speaker.. i need to know if its beeping

[jcarle]

There's only one thing you can do... disonnect everything from the motherboard (even USB devices) keep only front panel headers, cpu, memory and power supply, then see how it reacts.

[D_block]

yes there are speakers but no beeps at all, even the molex connectors arent even power other devices like the cd rom etc when its hooked up properly .. i tested the power supple else where and it working also tried a new one on the same unit with the same problem , i removed the cd rom tried it on another unit and it worked perfectly , so i was guessing the motherboard too , but its the 3rd time this pass few months ive encountered it ,im just baffled as to what will cause it to act this strange ????

i dont want to be a change parts technician but rather understand and explain to my customers what and why this happens etc ...

[infiniti25]

if you are trying a newer power supply on an older motherboard (example 3yrs old) you might have the same issue I ran into with a customer's machine.

I suspected the motherboard was dead as the computer turned on for a second and then shutdown completely. I tested with another power supply(new less than 2 years old) and it wouldn't even turn on for the second it has done.

So off I went and ordered a replacement motherboard (socket A) and hooked it up to my new power supply and again it wouldn't even turn on for a second.

I went and took an older power supply out of a known working socket A based machine and up it started. I hooked the same power supply up to the original motherboard and that too started and worked fine.

The only thing I traced on the net was that there is an optional -5v wire which is white on the 20 pin motherboard connector and some/most older boards require the power supply to have this wire. Most if not all newer power supplies do not have this wire since it is an optional part of the ATX specification.

I suggest you check your original and newer power supplies for the white wire and I think you will find the original power supply has the white wire and is dead and the newer power supply doesn't have the white wire and is fine.

I also suspect the mobo is fine in the eventuality that you have the optional -5v white wire problem like I did.