Check if there is a backup name "config.xml.bak" in var/config/ directory. If yes, rename the problematic one to another name, for example, config.xml -> config.xml.bad, then rename the backup one to config.xml, start the server again and see if it works.

Seems to me, you have a wrong definition in config.xml, so paste tomcat module definition will be helpful to determine what the problem is.