I do this for a living, you need to do what I have told you to get the thing working and once it works it does so for a very long time. I have systems out there from 2005 that are still working with out any intervention since commissioning.
Turn off dhcp on the DVR and use static settings, port forward on the router as you have done. Then open a no ip or dyndns account and set up user names etc, then find the page on your router for dynamic dns and put in the settings specified by the no ip or dyndns account.
Following these steps and completing them successfully will allow you to remotely view your CCTV system.