Sounds like you're using the PC as a bridge connection for the laptop to get out to the internet. A better arrangement would be to use a router between the cable modem and the computers. Each computer would hook directly to the router and would be able to access the internet without depending upon having the other computer turned on. A 4-port router is pretty cheap - about 40USD - and comes with a setup CD that pretty easily configures the computers on the network. Linksys and Belkin are two popular routers here in the states for home networking equipment. Adding a router has the additional benefit of built-in firewall called Network Address Translation (NAT). The "outside world" only sees the IP address of the router and not the IP addresses of the computers on your network.
Paul
I know that this does not address your immediate problems but I agree with Paul about adding a router to your network. I think that it would actually simplify things for you and be more robust and secure.
I currently have a network at home with a Linksys Router (BEFSX41) and 16 port switch (EZXS16W) supporting 6 PCs a couple of network attached hard drives, two printers, scanners, etc. all accessing the internet via a cable modem. The setup and maintenance of the network is relatively easy. The router is a DHCP server which means that it assigns the IP addresses to each of the PCs and administers the network. There is very little for you the user to do after it is setup. Adding a PC is not much more than attaching to an open port on the network.
Just a suggestion and maybe an inappropriate one at this time but worth considering after you sort the current problem out.
Larry
