While there are a myriad of reasons why your ASP.NET C# might not be working after a clean install in Linux, there is a very common problem that will prohibit Mono from working because of version 2.0 vs 4.0 issues. Typically this occurs on source code installations as opposed to package installs (particularly in CentOS / RHEL / Amazon Linux, not so much in Debian distributions).
You will see evidence of this crop up in your /var/log/httpd/error_log with an error message that looks like:
Cannot open assembly ‘/usr/lib/mono/2.0/mod-mono-server2.exe’: No such file or directory.
Fortunately there’s an easy fix.