step 2 the TECH uses a voltmeter and checks all wires on PSU for correct voltage.
PSU in Desktop dead, my guess fans dead too right>
you never said, what it does inside PC ,except nothing
does nothing mean dead silence?
the fan must run for 1second, then goes off.
a 1 second run tells me the PC power switch told the MOBO to turn on and in turn it tells the PSU to turn on,
the PSU then turns on for at least 1second,and if the voltages are ok
then the PSU stays on, else off goes.
15 and 16?
the 20 pin older supplies those are both ground
but 24 pin ATX pins are correct there.
the voltages are here.
There are 2 causes, of dead power button.
1: the buttons 2 wire cable ends fell off. at button or PC mobo.
2: The PSU is bad.
3: the MOBO is bad.
The mobo can also shut off any PSU, if the PSU fails
or it sees the regulators in the MOBO fail.
the Desktop runs on many power rails.
some in the PSU, others on the MOBO.
THe mobo creates special low voltage for the CPU.
the power good pin, does that #8,
One way to see if the MOBO is overload
is to remove things from it, I start at RAM
lacking a voltmeter, this is very hard to fix any thing electric.
only guessing or pulling objects PC can find shorts.
pull all power cables there, hdd, power, cdrom.
all things that use red/yellow wires.
all SATA cables, all USB , then ram. even a fan can short
a good tech keeps an open mind, and finds why the PSU shut down.
in most cases, the PSU is bad. but not always.
This is a feature, of ATX it keeps you from blowing up say a
$300 microprocessor.... or fancy gaming Video card (have one)?
yes, pull the video card too.