We have a client website which we inherited from another agency. It came with EE 2.10.1. We are normally a Craft agency, so we aren't unfamiliar with the way EE works.
Last night, I got a message that our client site was down. When I looked at it, the site started returning "File Not Found". This website was working earlier this week. I can get into the CP just fine. The log shows that the last login from our client to add content was on the 3rd. All of our other websites are working fine.
Can anyone tell me how I can diagnose this issue so I can fix it? I'm not getting any errors or anything.