Browser won't load admin pages

Not sure what triggered the problem, but recently most of my admin pages simply won’t load in Chrome or Safari (“This webpage is not available”). Firefox tries to download the php files. Some pages work, but posts, menus, library, plugins and some others give the error. I tried reinstalling Suffusion via ftp, but the problem remained. Renaming my plugins folder so no plugins are active didn’t help.

I would assume this is some kind of apache/server problem, but if I change my theme from Suffusion to the wordpress default theme, the admin pages all work fine. Site looks fine on the front end. Any ideas? The domain is https://www.gfinsf.com if that helps.

Thank you for your help.