I couldn’t open up existing documents after I upgraded to windows 10, so I upgraded Libre office to new version and still no joy, it just hangs
The combo of LO-5 & win10 appears to be an utter dog.
You can try Resetting to a Default Profile (Q56338).
LO-5 is from LibreOffice Fresh & as such may be buggy. You need to get used to using Bugzilla (or the Bug Assistant).
One alternative is to use LibreOffice Still (more stable, less exciting).
If this helps then please tick the answer ()
…and/or show you like it with an uptick (∧)