Fixed it! The C-States option under the Performance settings was turned on. Switching this off meant that the system restarts as expected following a power failure. I hope that this helps someone else.
I have recently bought a refurbished Optiplex 7040 to use as a home server. I've updated the BIOS to the latest version, shrunk the Windows 10 partition and installed Debian 11. All works perfectly - I can boot to Windows 10 or Debian 11 and everything works fine. I have been trying to configure the computer to auto power on after a power outage. I've set what I think are the required options in the BIOS. Normal booting still works fine. When there's been a power outage the computer does power up. BUT, it shows the DELL logo as part of the POST / BIOS loading and just sits there. It gets no further, no option to choose the OS or booting to the default OS. The disk access light blinks a continuous on/off pattern (same amount of time on, then off). Switching it off again, then on and it boots fine. I've looked on these forums and have seen people say to switch off Fast Boot. I did this in the BIOS and in Windows. It does not appear to have made any difference. Can anyone make any other suggestions? Thanks
Auto power on won't pass DELL logo on boot