Everything broke down :(

I use Scrivener since 09.2104, and never have any problems, until yesterday.
On Tuesday I installed Sierra on my Mac.
Yesterday I worked with my projects on Scrivener and everything seemed to work fine. But suddenly one of my projects looked very strange. Draft and Research sections retained their structure and names, but when I opened any document, irrespective of which section it appeared that it had no content. I closed Scrivener and opened it once again. But this time it crashed completely. On my Dock it has strange icon - white crossed circle in front of Scrivener standard icon. You can’t open the programme any more. I get the following message:
You can not open the “Scrivener”; It may be damaged or incomplete.
When I’m trying to open existing projects, that worked during the day I get the same message.
When I’m trying to re-install Scrivener (to the version 1.54) first of all I get the message:
Could not open the project. No valid Scrivener 1.x project could be found at the specified path.
Also I cannot use my serial number because I got the message that is incorrect (I bought my Scrivener on 9.9.2014)
My all project files aren’t on my main hard drive but on the flashcard. But I don’t know if this is the problem, because it worked well til now.
I don’t know what to do and where to start. I hope that I provide all informations.
Can anyone help me?

Version 1.54 was released in 2010 and it hasn’t been updated since then, and is a code base that goes back to 2006. If it runs at all on 10.12, it’s through sheer luck. Even a version as “recent” as 2.5 would probably be a bit of a gamble.

Are you sure your serial number is for the legacy version? If you’ve been using the program since 2014, version 1.x would have been old even by that point in time. I would try downloading 2.8 from the main webpage and see if your registration number works in that (if you even have to put it in, it might already be unlocked from before).

2.8 has been tested for 10.12 and should run fine. It’s a good idea to keep your software up to date if you subscribe to Apple’s yearly OS updates. They tend to break stuff, often, and we put out releases to fix those problems. That’s why I wouldn’t trust a copy of 1.5 anywhere near important work on Sierra.

You should always have more than one copy of your project as backups, that is the main objection I would have to that scheme. If you have been using 2.x and just mistakenly downloaded 1.54 recently, you probably in fact have backups of your projects on the main drive. Once you get it running, click on the Backup preference pane and click the button at the bottom to view your backup folder.

Given things got a little crazy, I’d consider copying those backups to a separate location just in case you need them.