I have an older sysem (i7 2nd gen) I was using as a storage server. Tried to install Umbrel, but after putting in the USB with umbrel flashed, and specifically set to the USB as the boot option, the screen stays black.
I’ve tried different monitors, and just booted the USB on my main PC to check and the USB installer does show up on there. Also tried setting boot mode to UEFI (was on legacyu by default) and that did nothing. It had Ubuntu server on it before which worked perfectly fine.
Any clues?
If you have it in UEFI, try disabling the Secure Boot thru the bios setup. That worked for me.
I don’t see an option for secure boot, so would I be safe to assume my motherboard doesnt support it. I wouldn’t be surprised as it is an old 2nd gen intel dell OEM mobo (inspiron 660, but with a i7-2600)
I’ll try seeing if turning a few other switches work, like the usb boot one, maybe umbrel makes it show differently? Kinda picking at tiny things now. Let me know if you have any ideas 
Update
I’ve got to the installer… somehow! haha No idea but UEFI was right and it didn’t hang this time so fingers crossed the install works
I got an old computer and was facing the same issue, I solved it also updating the date and time in the BIOS that was 2008.