Hello friends!
There is something wrong, and I cannot figure out what. The situation is such: every time I start the computer, it starts booting, but all of a sudden it gives me this kind of notice (all over the screen):
[ 25 .78435] hub 2-7.4:1.0: hub-port_status failed (err : -32). The last row says: [ 25.722189] hub 2-7.4:1.0: activate --> -19.
Then nothing happens until I press S, after that the booting process proceedes.

When I boot into recovery mode, I get this: Disk station /mnt/ usb-ST350082_OAS9A44 FFFFFFF - 0:0 - part1 not yet ready or cannot be found. Go on waiting or: press S to surpass the connection or M for manual recovery.

If I press S the booting will eventually succeed, if I press M the computer asks for my administrator password and then I'm stuck because I do not know what to do.

I managed to find a folder with the name /mnt/ usb-ST350082_OAS9A44 FFFFFFF - 0:0 - part1, it is empty.
What will happen if I get rid of it? Will the problem be solved or will it be vorse?

The most common reason I have seen for that message on boot is if there is an entry in the /etc/fstab for a flash drive or an external device and that device is not attached/plugged in on boot. Check the /etc/fstab file for an entry with that name. If it is there, put a hash mark (#) at the beginning of the line to comment it out and reboot to test.

Thanks for your help!
I tried that, but did not get any improvement. Instead I found out that my external disk, which I use for backups was not mounted when booting. That was one thing that the computer suggested, also ("could be something wrong with the usb cable"). I just did not understand what to do, but after switching to another cable the disk mounted normally (which it has not done for a couple of months, I found out). Now I'm able to get backups again, did not see that failure before. There is still a notice of a problem when booting, but it goes away quite quickly and the booting process proceeds normally, so I guess this can be marked as SOLVED...