Hello to all of you,
this is my first post, so at first I want to tell that my english is probaply not very well and (even worse) I'm no expert in Linux or Ubuntu. I use Ubuntu Mate 20.04 for more than a year now and I like it and it's working well.
But today it appears that my Seagate external hard disk cannot be mounted, the external audio interface neither. Both are connected via the USB ports.
I don't know what to do. Since both, the hard disk and the interface, are affected, I would assume something is wrong with the USB ports?
Any help is very appreciated, thanks in advance.
UPDATE: When I start the computer as an admin, I can see the other drives. But when I use my usual user name (also customized as an admin), they were gone. Right now I restarted again with my user name - they are back.
So the problem is kinda solved. But what could have been the cause for that problem? I'm grateful for any help, because if the problem would come back, I can use a little help, not just re-start again and again... Thanks 
Cheers,
Tom