We recommend open a port 24732 for normal sync / coin mining and had better a static IP !
Check your port 24732 on the websites:
http://ismyportopen.com 
http://www.checkmyports.net
http://www.yougetsignal.com/tools/open-ports
Ask questions your internet provider, what type of your IP (static or dynamic)?
Do you have port 24732 with open access?