I used to share my internet connection, without my router, through the Sharing panel of System Preferences. After messing around with some of the settings, laptops are no longer able to connect. These are the currently configured settings:
Share Connection From: Built-In Ethernet To Computers Using: Ethernet, Airport
Kinda slight on details. What happens when the laptops try to connect? Which network did the connect to before (SSID)? Do they still see the same SSID advertised now? I will assume your mac can still connect to the internet?
Is your laptop being asked to authenticate when attempting to connect? Maybe delete the network connection on the laptop and start fresh. If it authenticates, does it get an ip address? What software is on the laptop? Any Firewall? Can you ping anything? Can you surf by ip instead of name?