LO cannot open at all! What can I do?
“…cannot open sheets…”?
“… cannot open at all…”?
What did you actually try? What did actually happen then? (Please don’t talk much about what not happened except it’s obviously relevant.) On what operating system are you (also version)? Did you install/uninstall anything recently? Was there a crash? When did you last use LibO without problems?
Using Win 10 Home, opening a sheet from explorer list, nothing happens. I installed LibO 5.3.7 recently again, because after updating download LibO 5.4.4, calc sheets showed no lines and background colour anymore. It looked like unformatted. There was no crash. I used LibO normally just until it would not open anymore.
You may anyway try a new installation of a recent version.The current V 5.4.4 seems rather stable and reliable.
(Edit regarding the recent comment by the OQ:)
If the attempt to open a document from a file manager (in Windows by a doubleclick e.g.) does not call the correct application for the purpose, this is supposed to indicate a corruption of the file associations kept by the operating system. The installed software cannot do anything about this, for the very reason that it is not called, and thus not informed of the problem. Concerning windows issues of the kind were recently reported to be caused by one of the frequent updates of that jelly. (I also experienced problems - of a different kind, though.)
If your system hasn’t deeper lying problems a fresh install or a second run of the respective msi can do the repairs. Don’t simply clich the OK while the install is running, but read the prompts and consider them in this case.
From your other question I suspect you tried a downgrade without a prior full uninstall. This is not expected to work.
First of all you can check the situation by opening LibO without calling a file - and then opening a file via the ‘File’ > ‘Open’ menu path. If this dos not work, a new install is needed. Uninstall first and try to use the Win software manager for that.