I get a device error when booting into my OS. The boot hangs between 1 to 2 minutes due to this error which is ridiculous. In addition to that my system will no longer reboot at all. I can shut it all the way down successfully but then need to turn my power supply completely off and then back on before it will boot up again. The "reboot/restart" command no longer works at all. Very likely this is two separate issues but I'm uncertain.

I would appreciate any help anyone can provide.

This is the boot error:
dev-disk-by\x2duuid-3a0ee4f6\
x2df80e\x2d4a9c\x2db761\
x2d619fafb0f714.device:
Job dev-disk-by\x2duuid-3a0ee4f6\
x2df80e\x2d4a9c\x2db761\
x2d619fafb0f714.device/
start failed with result 'timeout'.

This is my system:
Operating System: KDE neon 5.17
KDE Plasma Version: 5.17.4
KDE Frameworks Version: 5.64.0
Qt Version: 5.13.2
Kernel Version: 5.0.0-37-generic
OS Type: 64-bit
Processors: 4 × AMD Ryzen 3 1200 Quad-Core Processor
Memory: 7.8 GiB of RAM

Thank you ahead of time,
Jeff

This is not a Grub boot error but is issued by the part of systemd that mounts all filesystems in /etc/fstab. One entry in fstab refers to a filesystem with UUID 3a0ee4f6-df80e-d4a9c-db761-d619fafb0f714, but no filesystem with this UUID is attached to the computer. It could be that the filesystem was removed or overwritten, or that the storage device is faulty.

Solution: Boot into rescue or emergency mode, then fix /etc/fstab. If it turns out that you have a problem with the storage device, you need to replace it.

How to boot into rescue/emergency mode depends on the distro that is installed on your computer. There are probably several methods.

I may not have been clear enough, but the system does boot and I can get back into the os (regarding the second issue of no "reboot/restart") But I have to turn my power supply all the way off and then back on again before I start the pc using the power button every time.
Does that change the way I can edit the fstab? Can I just open it from the file manager and look for that device or what? And also, what about the no "restart/reboot" option?
What on earth could be causing that problem?
Thanks,
Jeff

Yes, you can edit your fstab using a normal text editor when the system is running.

I would guess your disk (you have only one disk?) is reset each time you power off your PC, and that it is left in an unusable state when you merely reboot. Thus, a hardware problem. How hard is it to try booting from a different disk?

You may find relevant information in your kernel message buffer, which you can access using the dmesg command. I would look for messages that contain parts of the above UUID, or the string "sd" (SCSI Disk).

is this after the system hangs? If yes then probably related to fstab problem. At the grub menu is there a menu entry for recovery mode?

No. The systems hangs once started up.
The other issue is that I need to completely power off the system ("shutdown" & flip the power supply switch off too).
Only after fully powered off and supply turned back on can I start the system.
It then hangs at that error for a minute or two before loading the OS.

I actually have 4 hard drives and multiple OS's active.

Thanks,
Jeff

Use commands like blkid or lsblk -f to see which disk has this UUID. If there is no such disk, you can remove the corresponding entry from /etc/fstab. If there is, you can also remove it, but you need to be aware that this filesystem will then not be mounted automatically.

My guess is that you don't have such a disk. Perhaps the mount point in /etc/fstab gives you a clue what it is or was used for.