Z97 ASUS MB Problem

[FokMeLyf]

Hi, 

couple of things to say before i start:

1-english is not my first language, i'm fluent, but i'll make mistakes regarding grammar and sentences for sure

2-First time posting on a forum so if i do something wrong or post in the wrong place please let me know

3-I am no professional, don't have an engineering degree

 

So...

this is the second time i encounter a problem like this. First was in 2015, my z87(msi i believe) stopped working(had power, black screen, no bios) so i took it to a repair shop and the guy told me i had a bad MB and bad CPU... 600 euros to replace(i7 4770k and z87). I suspect the CPU was good, but I paid and it ended there.

Fast forward to may 2020. Now i've been assembling pc's for 5 years as a hobby and most of my friends rock a machine i built and they all work more than fine. 

I enter a small store and start chatting with the owner. He tells me he has an asus z97k with the same problem my z87 had 5 years ago, gives it to me telling me I can do literally whatever i want in order to fix it, including replacing SMCs(which I am still learning how to do even if I have all the tools necessary).

So far I spent 3 hours troubleshooting it with no luck, here's what i know and i have done: (MB that doesn't work is still an ASUS z97-k)

-The MB was working fine and a day decided to stop working. No idea if there was a power outage or the guy who owned it tried to update the BIOS and failed

-MB has power and beeps 1 time while turning on when i short the pwr pins

-I installed an i5 4670(maybe 4570, if i have to take it out i'll tell), known to work

-I installed one 4GB g.skill (1866MHz) stick of ram and i have 3 others. They are known to work

-using a shitty 300w PSU recovered from the same preassembled(is this a word?) asus rig that had the i5

-The MB has been tested by the store owner

-I have cleared the CMOS with and without the battery, then replaced the battery and repeated the process

-Used both the vga and HDMI ports on the back of the MB

-The monitor powers on, receives signal, backlight on, black screen 

-I don't have a graphics card installed, dont have a spare one to use, only a 2080 super in my main rig and I don't wanna take it out

-I have plugged a usb stick with the bios file(.CAP) both before and after powering on with no result(maybe i've done it wrong)

-The MB shows no apparent damage, components look fine, no funny noises 

 

Maybe the way i wrote it down makes it a little confusing so I'll summarize it here:

MB powers on, beeps once, cpu fan spins some times fast but always settles down after 10/15 seconds, monitor turns on with a black screen and I cant get into the BIOS

 

Pls help, I need to know what is wrong with this MB so I can sleep at night. I don't even care if I can't fix it, I just want to know wtf is the problem