16 hours ago
I will try to make this as concise as possible.
Nothing I do seems to change the boot from HDD problem, but it seems to work normally from the USB stick.
I know the basics of linux, but I am not super familiar with low level fixes.
Any suggestions on where to go? Reading the forums suggests it might be the old graphics processor (no external card, just the VGA built into the motherboard) but it works from the stick, suggesting the graphics is ok.
20 hours ago
So before I saw this answer, I somehow accidentally fixed it. After booting to recovery mode, I did a system summary, then I decided to look at the flash option since I'd never tried it before, don't have a file to burn. I expected a cancel option or some such, but the only one was power off. I changed nothing, saved nothing and pressed power off. The recovery menu reappeared, then console lines started overwriting the menu in random fashion, then it powered off. Powered it back on, and all of a sudden it is working. I've booted several times now and it seems to work fine. I really don't like it when this kind of thing happens, but I'm not inclined to go digging and risk breaking it again. Thanks for your suggestions. I may go look at /etc/gdm3/custom.conf but not sure if I'll change it.
6 hours ago
You may have a problem with an older computer, with an older GPU. Try this...
sudo mount -o remount,rw / # to remount the disk r/w
sudo pico /etc/gdm3/custom.conf # edit this file
Based on additional information from the user, I'd recommend that we check the file system to make sure it's ok.
To check the file system on your Ubuntu partition...
sudo fsck -f /
If for some reason you can't do the above...
sudo fsck -f /dev/sdaX