Sites on Apache2 suddenly stopped working, how to find the problem and fix it?

Question

Apache HTTP Server

Hello. Sites suddenly stopped opening. Worth Apache2. It seems to work without errors. However, the sites do not work. I did not change the settings, I did not touch anything at all. Just took it and stopped working. Absolutely all sites ...
Tell me, how can I find the problem? Advise

Answer 1

In general, I changed the IP - everything worked. What could be the problem? Maybe dudos on the IP address? How can you check?

Answer 2

1. restart apache
2. restart nginx
3. restart mysql
4 . Apache logs
5. Does site.ru/robots.txt open (static files)
6 Logs to the studio.