I did network update and now I cannot access my site

My WordPress multisite is set to auto update wp. It recently updated wordpress and everything was fine. I went in this morning and updated the plugins and everything was fine. Next I pressed the update network button and I could see the individual sites updating, listed 5 at a time. A large number were competed and then suddenly I am getting an "Error establishing a database connection". Please advise on how I can fix this.
Thanks,
Cathy