I just had a problem with my computer and now I can't copy and paste in Libre office

I just tried to open a downloaded .docx document, and my computer couldn’t open it and libre office quit (I usually can open .docx so there must have been some problem with it).
Now every time I open Libre office it comes up with a window saying
The last time you opened LibreOffice, it unexpectedly quit while reopening windows. Do you want to try to reopen its windows again?
It doesn’t go away whether I click on ‘yes’ or ‘no’ and I can’t copy and paste in Libre office.
I’ve tried restarting the computer and no change.
I’m afraid I’m not sure how to find out which version of libre office I’m using but I am using a mac os x 10.8.5
Any suggestions?

Please have a look at LibreOffice startup always asking reopen windows, and try the workaround.