Try starting the server manually, from the command line. This will give you direct exposure to the errors or issues within. To do this:
log in to a terminal session as your non-root user, often mc.
In this example testing is the servername, change as necessary.
mc@mineos-tkldev ~$ cd /var/games/minecraft/servers/testing
mc@mineos-tkldev .../servers/testing$ which java
/usr/bin/java
mc@mineos-tkldev .../servers/testing$ /usr/bin/java -jar minecraft_server.1.7.9.jar
The error you get here should explain why no servers start, whether it’s a java issue, jar issue, permissions issue… etc. If you share the output, we can help you interpret it.