If you are not already logged into your machine, log in (ssh if necessary) and open /etc/php.ini. If you're familiar with vi:
otherwise you can use
You should find a line that says short_open_tag = Off change this to:
short_open_tag = On
If the line doesn't exist just add it.
Depending on your machine restart apache. On Centos you can run:
After restarting apache you should be able to use short tags.