Toughbook CF31 : 1 led & no boot

Hello all,

After 2 years of good work, my CF31 (CF31ACBNNPM) can not boot anymore.

At start, 1 led lits, then after around 10 seconds fan is starting at max speed and black screen.

After consulting previous post, I tried with battery only, sector only, then without battery, HDD & RAM.

Toughbook reaction is the same in every case. I'm starting to fear a sudden death motherboard.

Any idea?