That warning should give you the option to continue. If there is something urgent you need to do, you can probably do it.
I think you have a rogue .lock file. With OpenOffice shutdown, open any folder and enter
%appdata%\openoffice\4
in the address bar near the top. That should take you to a folder that contains a folder named
user. Set that folder to show hidden items. You do that by going to the View tab and clicking the Hidden Items box that is highlighted in the image in
this post. You should then see a file named .lock. Delete that and the warning should no longer appear.