Thanks.
I know the drive is working, since I tried a lot of these shortcuts(?) by resetting SMC and so on and eventually I got into my MacBook, logged in and everything seemed as it was before. Same background picture and so on. Then I tried to update it, but that just resulted in a stop sign.
Back up the data as soon as possible. Then you can try playing with the system and decide what you want to do. If it fails while backing up get an external enclosure since is sounds like the data is there. And once you have the data backed up you have a number of options you can pursue without having to worry about data loss.