What do I do if my HP Z840 won't boot up?
Press and hold the power button until the workstation turns off, then press it again to restart. If this doesn’t work, insert a recovery USB flash drive (if available) and use F9 in BIOS startup menu to select the USB device as the boot source.
From the official HP Z840 Workstation manual, page 34
Have a follow-up question?
Answers from the official manual.
Common questions