Hi, Thanks for your reply.
I actually don't get any error on error.log
I haven't edit any apache config files at all for a while.
However, when the interface stopped working, I tried to access using ssh and saw that 46 packages can be updated. and 31 updates are security updates.
I tried to update the server and It didn't update either (if the problem is relevant somehow).
As I said, my domains are working fine and I can access the database too.
Please let me know If I can provide more information