"Yes, I have a second connection I'm trying to share on one of the computers."

This statement in particular is a bit confusing. Are both PC's connecting to the laptop, and the laptop is the host for your internet, or are you trying to daisy-chain laptop-> PC1->PC2? Ideally, your laptop should be setup to work as a router, with an ethernet line to a hub/switch that the PC's connect to with ethernet.

If that is your topology where your laptop is setup as the central router, then it may be an issue with firewall or port forwarding. If you forwarded ports to PC1, all data is likely being sent to that PC1 and none to PC2. Port forwarding shouldn't really be needed with the latest implementations of NAT--that should really only be used as a troubleshooting step to isolate an issue with ports being blocked. You may need to set a rule to enable/allow the ports to all IP's, as it can become problematic when you lock them down as a forward to one specific IP when you need it to go to other IP's as well.

You may fair better to get a wireless router and set it up as an access point to your internet source. This may streamline things much more in regards to performance, configuration complexity, as well as energy consumption.