[SOLVED] Computer isn't turning on despite replacing motherboard and PSU seems fine

[The Domino]

A while back my computer suddenly made a whining noise and turned itself off, now it wont turn back on, occasionally when I press the on button all the LED's will flash for a split second. I bought a PSU tester and plugged it in, it showed the correct voltages and showed green LED's meaning the PSU seems fine, I also connected the two pins on the power supply cable to test if the fan would spin in the PSU, it did and from what I have read online this should mean it is working fine. I bought a new motherboard and installed it and still the same problem. Is the PSU dead? I have ordered a new PSU however I was wondering what I should do if that still doesn't solve my problem, I cant think what else it could be.
Any help would be massively appreciated

 

[rgd1101]

full system spec? include make and model of the psu

 

[The Domino]

full system spec? include make and model of the psu

GPU - MSI GTX 970
Motherboard - MSI gaming 5 z97
PSU - Corsair 750W (can't remember exact one as was build 4-5 years ago)
RAM - Corsair ddr3 2x8GB (again, sorry cant remember exact model)
Watercooler - Corsair H100i
2 x 120GB SSDs
1x1TB HDD
creative sound blaster Z PCIe Sound card
1x standard disk drive

let me know if you need anything more specific and I can find out, thanks

 

[rgd1101]

without cpu?

test with the igpu only? without any hdd/sdd to go to bios? without the soundcard?

 

[The Domino]

without cpu?

test with the igpu only? without any hdd/sdd to go to bios? without the soundcard?

Sorry I forgot to list the CPU, its an i5 4690k, I've tried it without my soundcard, I'm thinking its just my power supply is broken. I'll try igpu and without any hard drives

 

[Nemesia]

Yeah try connecting to the IGPU without any GPU seated in the slot and without any drives.