My Precision 7820 do not turn ON

Hi, 

My PC do not turn on.

I tried all the fixing solutions that i see on dell support (disconnect Ac cord, press button for 15 secondes, etc)

Power button is blinking 2 white, 1 amber. What i read in the manuel : PSU or System board

I press the black button behind PSU, fans inside pc and fan in psu runs and the green led turn on.

So System Board? this is Mother board i guess? I check on web and it looks discontinued.

what are my options ?

Thanks !