thanks for your quick response peter, but it didn't work.
it seems that there is no way back
i use indesign for a long time, but i never saw such a behavior before.
You can try an export to IDML, but I suspect it won't work either. See Remove minor corruption by exporting
Can you see objects in the Layers panel? If you can , make a new doc the same size, then try selecting an "invisible" object in the layers panel, copy, and Paste In Place in the new file.
as you said peter: it won't work
@objects in layer: unfortunately no.
seems, that i have to rebuild the doc or parts of it.
what is the best way to prevent such things in the future? using cloud storage (with included versioning)?
What version of ID and OS are you using? If CC 2015, you might want to go back to CC 2014 (see How to Find and Install Previous Version of Adobe Apps in CC 2015 | Adobe Customer Care Team ), and be sure any version you use has the latest update installed.
The cause of this kind of error is hard to determine, but non-adobe plugins are a possibility if you've got any installed in InDesign. Security software is a possibility, too. Working with versioning in a cloud storage is a good idea, but don't use Adobe's. Lots of users here recommend DropBox for this.
i use ID CC 2015.2
but i think to go back to a further version will not solve the problem.
i've started with a new document and i hope, it will never happen again.
i work with gdrive and i have to think about buying more space!
thanks for your help peter
oh i forgot: WIN10