go to your LAN connection in network settings, right click and hit properties, go to the advanced tab, and check off internet sharing to be enabled. its in the properties somewehre i think in advanced. see if that works.
EDIT: your LAN connection is like whateer you use to get online. in network settings it should say Local Area Network connection or something as one icon and wifi connector as another one i think, but anyway just concentrat on the LAN one first.