Your dyndns domain just points to your ip-address, so to access your servers from internet there is no difference using dyndns or your ip.
You need to properly port forward your Router and that everything is routed correctly. Make sure you set your computer/laptop to a STATIC IP address off of the router. This is something I struggled with when I first started (including an FTP server). On my D-Link routers, it is listed under DHCP and I add my laptop MAC address to a "static client list". Then I port forward to that static IP address.
Standard ports (i.e. 80 for HTML and 21 for FTP) are blocked on the ISP end (want you to upgrade to business), so changing the port is mandatory. I recommend a dynamic DNS with a webhop. Then you do not have to add the port to the address, for those less techy like my parents.