Not booting even to see bios ZimaBlade x86 ZB001-BK10032

Hi,
I bought a ZimaBlade x86 recently, but it doesn’t start properly.

  • Power: lab PSU 12V / 3A
  • RAM: originally 16GB DDR3L → replaced with 8GB (from official shop)
  • Symptoms:
    • With 16GB: continuous buzzing sound, no display
    • With 8GB: short buzzing (2–3 sec) then silence, still no display
    • Tried miniDP→HDMI, then miniDP→DP → no signal
    • Now: completely non-responsive, only 0.11A current draw at 12V, no LEDs, no screen, no beeps
  • Tried CMOS battery removal → no change

Any suggestions on how to proceed? Could it be BIOS/board failure?