Suddenly locked out of admin and site not displaying correctly

I’m not quite sure on the version of WordPress I’m using as it’s been about 2 months since I updated this site. I have visited the site today and where the great black header is at the top of the page, there should be a background image. And the background was never bright blue to my knowledge!

Have I been hacked? When I try and log into the admin panel, I get this message:

A file permissions error has occurred. Please check the permissions on the script and the directory it is in and try again.

The web address is https://www.dogtrainersuk.com

Any help would be much appreciated