you have an Aurora R9

R9 oem motherboard proprietary LED controller header contains two pins for power switch.

to jump start, unplug LED cable and carefully short two pins transiently

R9 user reports pin 3 and 4.

Try eBay (USA) to replace the 0MF2N board

I prefer to think you'd be able to manually jump start the motherboard - powersupply on by keeping the LED header simply plugged in, then using a paperclip or staple etc, & momentarily inserting it into pin slots 3 & 4

Alternatively, disconnect the LED header, & touch 3 + 4 w/ a flat-blade metal tool (screwdriver tip etc) til it jumps on then reconnect the LED header

Alternatively use a paperclip-staple in the 24pin connector, in slots #16 Green (PSU ON) & #17 Black (Ground) , which is to say, jump those pins together momentarily long enough until the psu clicks on

@redxps630​ an aurora r10 to be precise. But what's weird is that I tried it once it worked . I powered  it off repluged all my cables and I did it again but when I tried it again. IT tried to power up for like half a sec and now nothing

@Cass-Ole​ so I tried to jump it with a screwdriver so pin 3 and 4 and nothings happening. 

in my experience, you need to reset cmos (by using the CLR CMOS jumper), then you can jump pin 3/4 again and it will work.  Weird.  in my R7 board transplanted into new case, I connect a reset switch to clear cmos pins, so I do not need to use jumper, and power switch pins to pin 3/4.  everytime I need to turn it on, I press reset once, then power sw.  try this.

https://dl.dell.com/content/manual25670963-alienware-aurora-ryzen-edition-service-manual.pdf?language=en-us

p.101-102

@redxps630​ so I did it with my screwdriver.
First the clr cmos jumper then tried the 3 en 4 pin nothings happening. can anything happen if i touch like pin 3 and 6 together for example ?

Just out of curiosity: how did you know the board is broken? 

I am thinking you might have a bad power supply, which would explain why jumping the pin's does nothing.

Try a BIST on the PSU: BIST test.

Above all, do not jumper 3 to 6 as that will short out your +5 volt rail...

use the jumper to clear cmos.  it takes longer than a touch of screwdriver.   recommended is 5-10 sec.