Hi,

15 trial days  might be over,thats why you are getting such a message. If you use only a single app, it will remain remain free for ever. But once we install more than one app, the days is limited to the 15 days, upon installation of the apps you will be notified about the same.

If you have to get back the db working, you can get in touch with Odoo and see what they says.

Thanks

Contact Odoo team

https://www.odoo.com/contactus