I have a motherboard, with the correct memory, and a CPU/cooler.  I also have a PSU, which SEEMS to work.

I put the bits together, connected a HD cable but left off the HD for the moment, and also connected a keyboard and mouse through a 2way electronic KVM switch (other PC turned off).

Turned on the PSU.  Nothing.  More in hope than expectation, pressed the (working) make-when-pressed button connected to the what I THOUGHT were the correct pins on the pin-array on the m/b : still nothing.

When I tested the psu using my psu tester, everything seemed to work; the fan started to spin in the psu.  When connected  to the m/b the psu fan did not spin, I think the m/b isn't firing because it is not receiving power, maybe other things too.

I did remember to connect the main power connector and the "P4" connector but that's all from the psu.

Why isn't it carrying out the POST ?  Why can't I CHECK the BIOS set up ?  That's all I want (until the next stage....).  What elementary thing have I overlooked ?

Dumb_Question
21.May.2015RAM...'with the correct memory'  = RAM

RAM in place.

If it were RAM that was the problem (which it might still be) I would expect psu to turn on, power to be received by the m/b, and beeps to heard (CPU fan, part of the cooler which I did not explicitly mention, to turn, possibly). 

I don't think it's RAM, but I'm hoping that it will be something as easy as that.  I connect the power switch between the pins described as 'power switch' but there is a another pair of pins on the same header which are CURRENTLY n/c described as 'reset switch'.

Dumb_Question
21.May.2015

 Then the reset and power wires are backwards...reverse them...
Also try with only 1 stik of RAM.Well, I finally got around to looking at this problem again (it doesn't feel like May since I did anything)

I can report that the PSU comes on, and I am now able to enter BIOS setup !

I apologise for wasting some persons' time with this issue as the solution was to use the correct jumper block (NOT the USB front panel one)

Now to connect a HD - O/S 

Dumb_Question
22.July.2015Wonderful...