Pages have disappeared in the backend?

My WP site is acting up. It’s an older version of wordpress. It’s 2. something. Try to go to the site and it is loading slow, http://www.claytoncommunityband.com. Also, sometimes the bottom portion of the pages don’t load. Furthermore in the backend, I cannot access a list of pages. There is just a blank area where the pages should be. The site has been fine for the last 5 years and is just recently starting to have issues. I can’t update any of the pages and the site only seems to work sometimes. Any ideas what this could be? Why would the frontend work occasionally and the backend not load the pages at all?