If the network card that ICS was enabled on still exist in Control Panel/Network Connections then you can simply right click on the network interface and select Properties then click on the Advanced Tab. Uncheck Allow other network users to connect through this computer's Internet connection.
If the network adapter is no longer present in the system then you could do the following
1) Take a system state backup of the machine
2) From a cmd prompt run: "Netsh firewall show config verbose=enable > fw.txt & fw.txt" (without the quotes) in order to get a listing of the current firewall configuration and rules.
3) From the cmd prompt run: "netsh firewall reset" (without the quotes) this will reset the machines firewall settings (including ICS) back to default. By default, ICS is not enabled.
4) If needed, then using the fw.txt above you could then re-add any customized firewall settings.