MongoDB doesn't start after changing the data directory
I ran into a similar issue and found it to be a misconfigured mongod.conf file in my case.  It could also be the permissions on the new directory are not set properly.  chown -R mongod:mongod &lt;directory name&gt; was how I ensured access (and of course the chmod 600 &lt;dir&gt; as well).  Lastly, run an ls -Z to ensure the context is correct.  I just compared to the default directory which worked for me.

If this is not resolved already, please show the contents of your log file as well.  There may be some clues there.