pc boot failure

Oct 4, 2018
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hi, i need help with a boot failure problem im having for the second time with my new build, ( everything including fan light up/rotate for a fraction of a second then shut down with " power led" on mobo indicating the pc is still in working mode)

these are my components i bought new from computer universe and build the pc myself.

Intel Core i5-8400
ASUS PRIME Z370-A mobo
Samsung SSD 960 Evo M.2 250GB
Sharkoon VG5-W case
Corsair Vengeance LPX Schwarz 16GB DDR4 Kit (2x8GB) 3000MHz C15
Corsair rm750x psu
an extra samsung sata 1TB hdd ( used part i added)
and also a used amd radeon r9 380 vga card

pc worked fine for a month or so then the problem started

Computer universe replaced my cpu and motherboard, under guarantee, as these parts seemed to be causing the problem. They didnt tell me which of the 2 had a problem. But got 2 new ones ( i assume! )

Now, i have the same problem again after a month or so, with the new parts i received from them.

I have checked the first time whether the psu was causing the problem as i also have checked today with an extra psu unit i borrowed but still no proper start up.

What could be wrong? Again the cpu or mobo? maybe viruses? molex not connecting well? overheated cpu during gaming? (55 degrees are not much are they? ) vga card incompatibility or drawing too much power?

tried everything, battery removal, removed all parts, reset bios pins etc...

please help, any advice?