Cannot install TrueNAS Core on Server

Hi,

I have a fujitsu server where I am trying to install TrueNAS on. Whenever trying to boot from the USB stick nothing happens. After the Post screen it just says "No Signal" on my display. The server is not the newest so it does not have UEFI or EFI boot. But I did install FreeNAS on it some time ago.
What am I doing wrong? Or is it just not possible to install TrueNAS on Legacy non UEFI systems?