My site started returning an Error 500 after my host did a server upgrade. I made no changes or additions to the site between when it was working and when it wasn't. If I disable the htaccess file and turn off clean urls, the site starts working again.
I've asked my host multiple times if anything was changed as a result of the server upgrade, and they said no. They suggested that maybe some part of my site had written to the htaccess file, but I have uploaded a new, clean version of it, and it didn't change anything. They said that maybe the software I was running or a plugin had updated automatically without my knowing, which I know isn't true. They said there was no sign of hacking, and told me to talk to a developer. Any ideas?