I install endeavour OS for different individuals, often on older hardware. Recently one of these computers, a Dell laptop about 7 years old that had been running really well shows an 'Invalid partition table! ’ error on a blank screen on boot.
From the little I know about these errors they often indicate a failing hard drive, BIOS setting errors, damaged boot files, or a corrupted partition table. I know the BIOS hasn’t been touched. I booted from an EOS USB drive in UEFI mode. fsck ran okay showing no errors. Also smartctl tests all passed. I don’t know what else I can do except attempt to reinstall EOS. That of course will take a little time and it will mean I will never learn what the original problem was Before I do that I’m wondering if I am missing something simple.
Any thoughts or suggestions?
It depends on during which phase in the boot process the messages come from.
Study (again?) the boot process article and try to get more debug messages for troubleshooting.
I suppose I should have written “on attempted boot” rather than “on boot”, because there was no boot process at all. Simply went immediately to that blank screen with ‘Invalid partition table!’ error.
I suppose you have not read the linked articles I have posted above, which means I wasted my time. It’s just sad.
Linux/computers terminology is not every-day language.
If you want help, you need to speak and understand the common terminology for the context you are on. 
Why would there be a specific page at the Arch wiki just to explain the boot process?
Petsam,
You didn’t waste your time. Rather you guided me to new discovery and knowledge. But it will be knowledge for the future. The person whose computer it is had immediate need for it and preferred I just reinstall the system. It is working now.
I hope you won’t let me or anyone else discourage you from trying to help people.
Thank you for the education and thank you for your time.
have you checked with parted or Gparted ?
sudo parted -l
sudo fdisk -l