HELP. 7700K won't boot on Z170 AFTER bios update

Hello guys,

I really need your expertise on that, it's driving me crazy.

Got my new 7700K to replace my old 6600K on my Asus Z170-A.

Did a bios update directly from the bios via the EZ software to the last version wich support kabylake cpu.

What happened is that after changing the cpu, the pc launches and ended up on a page wich tell me a new cpu has been installed and press F1 wich transport me to the bios in wich the i7 is detected but when I quit the bios all I get is a black screen.

Even after many reboot all I get is a black screen, not even the bios page, can't access anymore unless I put back the i5, boot, put back the i7 and then I can access it but once and once only.

Tried my i7 on another mobo, it works perfectly and my mobo works fine with the 6600K so I guess it must me bios update related?!

Really need your help on that one cause I tried absolutely everything I could think or read about.

Even Asus support is of no help.

UPDATE : I can now boot but I have to use the MemOK button on the motherboard everytime. Did a memory test but there's no errors, so one problem solved, another one to solve.