ERROR ESTABLISHING A DATABASE CONNECTION

I haven’t gotten any sleep over this and am just in tears. I was getting an error message that said: Error establishing a database connection and now it’s changed to “The page can not be found”. I had changed the password from an email that wordpress sent me to one that I could remember and had been working on my page all day.. logging in and out with the new password. There are a few other users that were listed as administrators. I could not make changes so I had to go in as an administrator and change mine to administrator as well to make changes. Several hours of working fine and all changes recorded then I got bumped off line and couldn’t log in with current password but just kept seeing the error establishing database message. I quit working on it out of frustration and a half hour later, I NO LONGER saw the error establishing a database connection message and was now able to log in with the old generated password and when I went finally logged in, the pages were all gone and it said no pages found. Also when I would go to add a new page as if I had to start all over, it gave me a message that said that I WAS NOT ALLOWED TO EDIT THIS POST. If I put in our company’s url address, the site is gone but all I see is our company header and under it is states page can not be found Apologies, but the page you requested could not be found. Perhaps searching will help. I don’t understand why it lets me log into wordpress but won’t let me make changes and site is down but no longer getting the error establishing database connection. It does show me as an administrator. I also noticed that when I try to add a new page, in now has a button that says submit for review instead of seeing the button like I use to that was and (update) button. I can’t create all new pages if I wanted to. I just want all my old pages back with the new theme I chose and new password. Please help.