Precision 3431 cpu upgrade

Hello,

today I wanted to upgrade the i5 of my Precision 3431 to the latest i9 9th generation i9-9900. I found a Core i9-9900KF for LGA 1151. The Precision is already set up with an AMD Radeon Pro card which is also set in Bios as the primary GPU. The machine is also running on the latest BIOS version.

I replaced the CPU with care but the machine isn't booting anymore after the replacement. When powered on the screens remain black; I only notice that the cpu fan is spinning with a constant speed.

Does the Precision 3431 not support "K" or "KF" versions of the Core i CPU's or are there any other preliminary steps to do before the CPU change? The original CPU is running fine.

I can also exclude a damage on the replacement CPU as they worked fine before in another of our workstations.

Thanks
Dietmar