Cannot edit a page I've been editing previously

I am using Sharepoint 2013, I am currently working a page but the "edit page" option at the top right has disappeared and when I click on the "page" option in teh toolbar the edit options are greyed out and a box appear when I try to click on edit. The box telling me that this function is currently disabled.

I am the sole administrator for the site and still have the edit function on all the other pages I have created. I'm working to a deadline so please help!

Thank you.