I have the same problem and I am running linux mint 22 and now 22.1 and this happens to me, from time to time.

As the screen is not readable, I hard shut down the Latte Panda Sigma using the power button. (The screen looks like the photo provided by DEV 1 .)

Then start it up normally hold the power button in, and it boots and works normally.

But this happens around once a month on average. And this has happened since I bought it around 2 yrs ago.

I am not overheating it, I am just using it as a desktop PC, You tube, Web Searches, Email. Sometimes the fan is on, sometimes the fan is off. I do very little else on this machine. It is dual booted to windows. Which I rarely use,  but it has done it while I have been using windows too.

I had a problem when I installed LINUX MINT 21.2 on the Latte Panda Sigma about 6 months ago. And I was scared about finding drivers etc, as the installation didn't work that well regarding communication ports etc. IT was a disaster, until I heard about updated kernels........

I discovered that if you changed over your kernel from 5.15 series to 6.1 series..... everything worked. Currently I updated to LINUX MINT 21.3 today, and the set up is using kernel 6.1.0-1028-oem. The 6.12 series of kernel is designed for the latest modern computers, while the 5.15 is for the older equipment....... and that's why it works on the SIGMA.

So what ever linux you are on, get the 'edge' version, or replace the 5.15 with the 6.1 series kernels...... it has worked very well for me. (and saves you looking all over the place for individual drivers) Every problem I had went away with the kernel upgrade..... good luck, hope it works for  you. I am dual booted with WIN 11.

(Copy and Paste of abridged system info, below)

System:
 Kernel: 6.1.0-1028-oem x86_64 bits: 64 compiler: N/A Desktop: Cinnamon 6.0.4 tk: GTK 3.24.33
   wm: muffin vt: 7 dm: LightDM 1.30.0 Distro: Linux Mint 21.3 Virginia base: Ubuntu 22.04 jammy
Machine:
 Type: Desktop System: LattePanda product: LattePanda Sigma v: N/A serial: <superuser required>
 Mobo: N/A model: N/A serial: <superuser required> UEFI: LP-BS-WTADLC1R210-C v: 5.27
   date: 05/09/2023
CPU:
 Info: 12-core (4-mt/8-st) model: 13th Gen Intel Core i5-1340P bits: 64 type: MST AMCP
   smt: enabled arch: N/A rev: 2 cache: L1: 1.1 MiB L2: 9 MiB L3: 12 MiB

I had similar problems when I dual booted my SIGMA to Mint 21.2 around 6 months ago...... bad connectivity and things not really working.

Then after some mental confusion, I updated the kernel from the normal 5.15 series for normal everyday computers, to the 6.1.0-1016oem for the new "hot" computers, like the Latte Panda Sigma.

Guess what...... it all worked well. Been using it fore 6 months with no faults, and upgraded to Linux Mint 21.3 today............ the kernel now is 6.1.0-1028oem. Still going without problems.

Good luck

System:
 Kernel: 6.1.0-1028-oem x86_64 bits: 64 compiler: N/A Desktop: Cinnamon 6.0.4 tk: GTK 3.24.33
   wm: muffin vt: 7 dm: LightDM 1.30.0 Distro: Linux Mint 21.3 Virginia base: Ubuntu 22.04 jammy
Machine:
 Type: Desktop System: LattePanda product: LattePanda Sigma v: N/A serial: <superuser required>
 Mobo: N/A model: N/A serial: <superuser required> UEFI: LP-BS-WTADLC1R210-C v: 5.27
   date: 05/09/2023

Have been using linux mint from the time I received the Latte Panda Sigma. It was a problem, with connectivity etc on the standard kernel. I changed the kernel in the system to the more recent 6.1 etc/whatever , and it has been working flawlessy from mid last year on LM 21.2, and upgrading it today to Linux Mint 21.3 (Virginia). Initially it had me stumped, until I found that they  had an 'edge' version, or leave it as is, but upgrade the kernels. Then everything bloody well worked as it should........ magic!!!!!!!

So I'm not sure what you have, but strongly suggest you do homework on upgrading kernels to the latest, or changing to 'your' linux with edge version kernels........ all the stuff at the top is a copy and paste of the beginning of my system description.... BTW it is dual booted with ther supplied windows, but that's not showing as I am on linux now.  Good Luck.

if you are multiboot (like me).... my LattePanda Sigma's start up menu is in this order:

* Linux Mint 21.2 Cinnamon

* Advanced Options for Linux Mint 21.2 Cinnamon

* Windows Boot Manager

* UEFI Firmware Settings

I can select what I wish to open by selecting whatever line with the keyboard up/down arrows buttons.

The first selection Linux Mint will auto start up after 10 seconds, or I can push the 'eneter' button for instant start,

BUT, if I select any of the 3 lines under the top line..... THE COMPUTER WILL SIT THERE AND DO NOTHING INDEFINATELY.... unless I push enter. Then there is immediate startup/selection of that partricular option.

So, If I want to select Windows tp start up....... once the boot screen is open and visible, I have to click down using the arrows buttons to select Windows AND THEN CLICK "ENTER"....

Windows then boots. Maybe it's the same on your system, if you O/S is down the list a little.??

Good Luck.

UPDATE 2..... re-installed LM 21.2 using a new iso (from Linux Mint website)..... over the top of the beta installation (first option in the Mint installer).

Have APTIK and did a full restore, to the re-freshed (new LM 21.2) installation.

Kernel reverted back up to 6.1.0-1016-oem...... then a few things happened all at once. Upshot is that I now have audio and network connection and HDMI Video/audio.

Lesson Learnt: I got my dirty hands on the beta version of LM21.2 and it had a few issues.

A week later, I installed the freshly released mainstream release of LM21.2, on top of the LM21.2 beta that I had issues with. (Issues were video/audio/network, sort of working a bit and sort of not really...??)

It all works well now........... good news for LattePanda Sigma fans who were wondering about Linux Mint 21.2 for their new pc.

The Windows 11 side of the dual boot also works well.

UPDATE:

in WINDOWS I have disabled fast boot.

in LINUX Mint 21.2,   (Which is now mainstream released a couple of days ago)

I have installed a later kernel, 6.10-1016-oem; and

added 'nomodeset' to the 'quiet splash' line in the BIOS startup settings.

The difficult networking connection and the hard to start HDMI video both seem to work consistantly now.  (I am connected to a TV used as the monitor)

 No audio seems to be my only problem now.

Hope some of this info assists any other dual booters out there....

Peter

My Bad  !!!!  (Duh). 

My Iso file was a combination iso and image. In Rufus there is an option to sort that out by creating (from your file) an .iso only. So I tried that, restarted the Sigma, and this time the bios saw the USB with file.

Installed Linux Mint 21.2 Beta which wouldn't work to begin with, so restarted in Safe mode, and clicked on repair packages and maybe network as the main problem was network not connecting.

Restarted the normal way, and it is completely working.......... with Windows 11

still working along side. Just select which O/S you want during start up. Happy now   

Adding to my initial post...... tapping on F7 to enter BIOS, and shifting to the BOOT Section....

                              I noticed that:

there is only one option in there... windows boot manager with SSD Brand Name and model. Just one option, and it is listed as 1. (no 2 or 3 or 4 is on the page)

NO USB or network option ( or anything else)

Those options should be there...... so how does one fix that for a start?