I dont know if Jon was able to fix the problem but what I have seen is that if one day suddenly services refuse to start up then most likely it has something to do with your IP address or file permissions.
Before digging deep into log files to find out what exatly is causing the failure, you can try two things:

1) If you are behind a router, make your IP static (e.g. 192.168.1.2). Put the same IP in settings as it was at the time of installation.
As root go to /usr/sbin/system-config-network


2) Make sure Oracle is the owner of all the files under oracle folder.
As root go to Oracle home /home/Oracle

Change owner and group to Oracle for all the files underneath it.
chown -R Oracle *
chgrp -R Oracle *

Hope that does the fix.