Lets start with the Linksys. The computers are able to get online using the linksys router? If yes, then get on a computer, open up a command prompt. (type cmd in windows 7 search box) and type ipconfig. It will show you the ip address, subnet mask, and default gateway of your network. Now print a configuration page on the p4015. On the second page, check if the IPs first 3 sets of numbers (example 192.168.1) match what the computer shows as its IP address. Then check the subnet and gateway as well. I am going to assume that you will find your problem right there.