SD is in and loaded only says "main" none of the files show up  

RE:

How old is your machine? Or more precisely, how many "cycles" of the SD card/card socket have been made? After several hundred, my socket began to be unreliable, as noted in this link. A response by @neophyl included a link to a socket "shim" that cured my problem. Maybe it will cure yours too. Of course if you can't get the card to be recognized at all, that's a thornier problem.

RE: SD is in and loaded only says "main" none of the files show up

Reformat the card. Plus,  I assume you're talking about gcode files. There have been similar posts here where at long last it turned out folks had put STL and 3mf files on the card and were surprised they didn't show up. 

RE: SD is in and loaded only says "main" none of the files show up

Agreed. I've also had the edge of the SD card (a tiny piece of plastic) come off and get stuck in the card socket. I blew it out with compressed air, then tossed the SD card. Fortunately, they are cheap, so keep a handy supply of them.  

RE: SD is in and loaded only says "main" none of the files show up

im using Ubuntu and somtimes i need to format the SD in a Windows system to make it readable in the printer

even on UNMOUNT and OR Poweroff it happens from time to time that the SD card will not be readable in the printer or in the PC Cardreader

There is a flag on the CARD that makes this trouble

sudo umount /dev/sdc1
sudo fsck.vfat -a /dev/sdc1
sudo chown -hR USERname /dev/sdc
sudo mount --options remount,rw /dev/sdc1

RE: SD is in and loaded only says "main" none of the files show up

Make sure it's not locked 

RE:

From the description you've provided, it sounds like the SD card is recognized by your device and is displaying the "main" message, but no files are appearing. This could be due to a few different issues, but the most common causes are either a corrupted file system or a problem with the SD card itself. In order to determine the root cause and resolve the issue, I would recommend trying a few different steps. First, you could try checking the SD card for errors by connecting it to a computer and running a disk check utility. This can help identify any problems with the file system and potentially fix them. If this doesn't work, you could try formatting the SD card to see if that resolves the issue. Just make sure to back up any important files before formatting, as this will erase all data on the card. Finally, if neither of these steps works, it's possible that the SD card has failed and needs to be replaced.

I hope these steps help resolve your issue with the SD card. If you have any further questions or need additional assistance, don't hesitate to reach out!

RE: SD is in and loaded only says "main" none of the files show up

I assume you're talking about gcode files. There have been similar posts here where at long last it turned out folks had put STL and 3mf files on the card and were surprised they didn't show up.

As @fuchsr posted above, the printer will only recognize gcode files. If you have other file types on the SD card, they will not show up in the LCD menu list.

If you have the SD card that came with the printer, and haven’t erased or reformatted it, try inserting that into the printer to see if the files show up.

Cheers

Try deleting the most recent file you added to the card; yes, I know that's the one you want to print, but is the card now readable?

If so, rename the file something simple like 'thing.gcode', copy to the card and try again.

Cheerio,