I had a desktop (win-xp) connected to a cable modem, a switch and a dlink router. The reason for the switch is because I wanted to use the desktop with xp without the wireless router being on all the time. I also have 2 laptops, one with xp and one with win7. I can use all three computers at the same time. I bought a new desktop with win7 to replace the xp desktop. When I hooked the new desktop up with win7, I can't connect to the internet with the two laptops while the desktop is on. I have to turn the desktop off and reboot the cable modem before the laptops will connect to the internet. When I want to use the desktop, I have to turn the laptops off and reboot the modem to get the desktop to connect to the internet.
What is causing this problem?
It sounds like you have your cable modem connected to your switch, and then your desktop and router are plugged into the switch, and then laptops connect to the router, correct?
Your cable modem should be connected to your Router, and then computers and switch to the router.
You will either need to leave your router on all the time, or go through this process each time.
Routers are designed to take your external IP and NAT it to allow multiple computers to connect to one IP address. Theres no reason you should turn your router on and off... if you're worried about security issues then you need to set those paramaters up on the router.