A Brief Note on Firewalls
Modern hardware routers often ship with fairly sophisticated firewalls built into them. If yours does, you may not need to use a software firewall, such as the Windows firewall, or the firewalls incorporated into Internet security software. In my home, we typically turn off software firewalls. Is that safe? We've never had an intruder get into our home network.
Most routers have logging capability built in, and checking those logs is always illuminating. When we look at the log for our home router, a D-Link DIR-655, we see a few entries that read like the following:
Blocked incoming TCP connection request from IP address xxx.yyy.zzz.123 to [router IP address]
I've changed the IP address above, and I've chosen not to reveal my router IP address for obvious reasons. What this can represent is a serious intrusion attempt, or some software bot simply pinging the router to see if the network is exposed.
No firewall is completely foolproof, but we've had good success with hardware firewalls built into modern routers. While the default settings are often good enough, many have additional capabilities for the truly paranoid. So if you're worried about intruders sneaking into your network, ratchet up all the settings on your hardware firewall.
I can offer some general troubleshooting tips here, but hardware and software combinations can vary widely. Be prepared to contact your ISP, your router manufacturer, or tech support for each piece of client hardware as appropriate. (For more tips, check out "How to Fix Anything.")
Can't set up the router: Sometimes, you can't even connect to the router or access point for initial configuration. Make sure you've connected to the correct port; some older routers may allow you to perform initial setup only by connecting to a specific port. Similarly, older routers and most access points may require a crossover ethernet cable.
In addition, you may need to first set up your PC for a specific IP address, and then reboot to actually connect to the router.
The router doesn't see the ISP: This often happens if the router is set to automatically receive an IP address from the ISP, but you've asked for one or more static IP addresses (or if you've entered a static IP address incorrectly). Also, if your modem doubles as a gateway, you'll have to configure your router differently.
The client hardware can't connect: Make sure DHCP is enabled. If you're using a Wi-Fi connection, make sure that security and encryption are set up correctly. For example, many laptops ship with tools from the manufacturer to streamline the configuration process. I've seen some of these tools incorrectly detect the type of security being used, so you may have to go to Windows' own networking utilities to set that.
Next: All Plugged In