Need to check your ISP allows static ip's. Some don't.
Setting up a Static ip is where most people get it wrong. But this 'must' be done first before port forwarding can be done.
I can tell you there's been many users on these forums using same brand & model of router with problems. Just discovered why, SURFboard SBG900 - Motorola. The Motorola SBG900 does not support UPnP thus needs to be port forwarded or port triggered.

Apparently the SBG 900 does have a firewall configuration to set high, medium or low. See page 27 of manual.
Motorola SBG900 Manual = http://broadband.motorola.com/consum...User_Guide.pdf (2.9 MB acrobat PDF file)
Port Forwarding on page 44 or Port Triggering p.48). TCP/UDP combined should be chosen. Port to choose, choose one between 49152 - 65535, such as 64049. Reciprocate this port in the LW advanced -> Firewall setting for connection & listening ports.

Verifying ip address, page 62 of manual. ie: 1. Start menu, 2. Select Run, Type cmd & click OK. 3. Type ipconfig & press enter to display ip configuration.

* Port Triggering is slightly different to port forwarding. Not sure whether static ip is required for port triggering but would imagine so because most of these settings are based on ip address of particular computer or user. However I do not see a particular ip address entry point. So perhaps this is an alternative option.

* One thing I discovered whilst browsing the pdf manual is you 'do' need to reboot the router for changes to take effect. (p.76 of manual) This used to also be true with my 'old' router.