Ubuntu Version:
24.0 LTS, Cinnamon
(I have two notebooks with the same ubuntu and same problem, one Dell, one HP.)
Some months ago I started getting the problem that ubuntu never completes the boot process; usually just hanging with a Ubuntu logo and spinning wheel. On both notebooks a hard power-off followed by immediate power-on usually solves the the problem, though the Dell can need 2-3 attempts. How can I solve this? Thanks.
Welcome to Ubuntu Discourse 
Does the problem persist if you boot an older kernel?
You should be able to access that from the Advanced options menu in GRUB.
Please post specifications such as RAM, disk type, and graphic cards.
Thanks. Yes, the problem persists on the Dell at least, running Linux 6.8.0-55-generic instead of the -56- current kernel.
First, for the Dell notebook, the details seem to be:
Notebook: Dell latitude 5340 Core i7 16Gb 512Gb SSD 13.27"
RAM : 16Gb
disk-type (from lshw): NVMe device, 2550 Micron 512Gb
Graphics card (from lspci): 0000:00:02.0 VGA compatible controller: Intel Corporation Raptor Lake-P [Iris Xe Graphics] (rev 04)
Now, my HP has a different setup, just 8Gb, SanDisk SD7SN6S-512G-1006, Intel Corporation Skylake GT2 [HD Graphics 520] (rev 07)
so both graphics cards and disks are differ. The cinnamon version is the same though - and both are updated on a near daily basis.
/Dave
Are UEFI firmware & SSD firmware latest versions available from vendor. Older system may have stopped updates, but may have newer version.
Compare firmware versions to vendors support site
sudo dmidecode -s bios-version
udisksctl status
HP’s typically require you to go into system settings (not UEFI boot menu) and change boot order to have Ubuntu first. If only booting Ubuntu, you may need to create an UEFI boot entry that says “Windows Boot Manager” but boots shimx64.efi.
man efibootmgr
sudo efibootmgr
sudo efibootmgr -c -L "Windows Boot Manager" -l "\EFI\ubuntu\shimx64.efi"
Hard shutdown can corrupt file system requiring a fsck. And grub has check that previous shutdown was normal, so grub menu should always then appear. Can you then boot recovery mode?
Does removing quiet splash on linux line in grub menu (default in recovery mode) show anything. You see boot process, which also is in logs. Errors often are not last line, but several above that.
You can check log files, but some commands have error in name, and many not related. I get a page of “errors” but have no issues booting.
Errors/Warnings:
sudo journalctl -b -p err
sudo grep -Ei 'warn|error' /var/log/*g
I am using Kubuntu on Skylake desktop & Dell 5310 with 11th Gen Intel. No issues.
Thanks. I’ll work through those ideas, but have never had to mess with bios or firmware before so need to proceed slowly (in between work sessions). My Dell is just some months old though, so should be up-to-date.
It could be also some kernel grub boot option need to setup if some uefi or apci bugs are present.
maybe:
vt.handoff
intel_iommu
or setup some video=some_mode
or force some acpi irq… 
on some broken acpi it helps, but recent have been make some progress so some new kernel or something could bring fresh air…
Thanks for new tips. I don’t really understand any of this I’m afraid, so haven’t dared do anything so far (stress from a work deadline also stops me experimenting much, or risking loss of PC). Would a simple re-install of another flavour of ubuntu (e.g. plain unbuntu) help? I ask that as it is very strange to me that two such different notebooks should develop the same issue at the same time. So maybe software rather than BIOS or hardware? (Still, I haven’t seen others complain of the same issue, so this is all very confusing).
If having system is that critical, you do have good backups?
With good backups, you can totally reinstall & restore from backups, and add back any manually installed apps in about an hour. Without backups you may not recovery or have to spend days trying to get some data back.
To really get help you have to tell us the results of suggestions we make.
Dell is usually good about firmware updates. HP updates thru Windows or manually, so it dual booting it will update, otherwise you have to download install firmware yourself.
I have excellent backups of my main discs, so a new install is easy enough, though I tend to avoid full re-installs when possible since I then have to mess with various tricks and settings to access remote computers and sites. The problem I have with the other suggestions (which I really appreciate!) is just that I have no experience of any of them, and would need to google and test for hours and likely days, and then risk my system. And often googling doesn’t help since I have no idea what to look for, or what the different terms or suggestions mean 
The only command I posted that would make any change is the efibootmgr to add a new entry. That would not change any existing entries, but would overwrite an existing Windows entry.
All other commands are just queies to see your configuration or errors.
Best to use man pages if concerned about a command.
man efibootmgr
man dmidecode
etc
If changing settings in /etc, you should be backing those up also. I edit grub, but put copy into /home so backed up. Some suggest backing up all of /etc.
I also have a few settings I scripted to edit fstab to mount data partition and do NFS settings. I do multiple test installs and sometimes restore /home from main working install or manually config to test different settings But I want same system settings and found doing them over & over was easier with a script. I found version update left too much cruft over time, even with lots of housecleaning.