Troubleshooting a home network can be a little spooky, especially if someone else originally set it up for you. Really, though, there's not much to it. Take it a step at a time, and take your time.
It helps to think of your home network as something other than a dizzying array of wires, cables, computers, routers, modems and such. Think of it as a garden. No, seriously. Think of all those ones and zeroes travelling through all those cables as water. Your computers are the plants. It's as simple as that.
Note that this answer will assume you're using a high-speed internet provider as your ISP (that's who you pay your internet bill to), which means I'm assuming you're using DSL or Cable. I'm also assuming you have very little experience in dealing with home networks, but have an open mind and are willing to learn something new.
Let's get started by mapping your home network.
We'll start with the water source. Somewhere in your house is a coaxial cable (if you have cable internet) or a phone line (for DSL) coming out of the wall, and plugging into a modem (usually in the form of a little black box with a lot of lights on the front). Grab a piece of paper and draw a little rectangle in the top center--that's the wall plate that this cable or wire is coming from. Draw that cable as well, going from the wall plate to the modem.
In our garden analogy, the modem is the water filter. The modem translates the signals coming from that cable into signals the computers in your house can understand. Plugged into the back of the modem you'll see three cords. One is the coaxial cable (or phone line) coming from the wall. The other one is the power cord (you don't need to draw that). The third is the cat5 (ethernet) cable, which connects to a computer (if you only have one in the house) or a router. Let's assume you have more than one computer in the house with an internet connection, which means you have a router.
The router is the water pump. It pumps the filtered water from the water source to all your plants (computers). So, draw the cat5 cable going from your modem to your router, then draw your router. Label your router with it's name and model number (e.g.: "Linksys WRT54G"). You'll be adding your router's IP address to this picture in a moment.
Now, there are two types of routers: wired and wireless. Most routers (even the wireless ones) have four ports in the back, where you can plug in cat5 cables. You use these to hard-wire computers in your house to achieve an internet connection. You may also have wireless computers in the house (such as a laptop or two). We'll sketch those in later.
Look at the back of your router to see if any computers are plugged into these ports. The ports are usually labelled 1 through 4. If there's a cable plugged into port one, grab that cable and follow it to the computer it's plugged into. Draw this on your network map. Repeat as necessary for any other hard-wired computers.
Now, look at your router's user manual. Somewhere in this manual (usually in the "Connect to your Router" chapter), you will see an IP address listed, usually in the form "192.168.x.x". This is your router's IP address--your network is like a neighborhood (if I can break my previous analogy for a minute) and every "house" (e.g.: your computers and router) has an address. Find the IP address for your router, and write it down on your map, next to the router.
Go to every computer on your network and (if you're using Windows XP) do the following:
Click the Start button, and go to Run. Type this in: cmd Then click "OK".
This is the command window. Looks a lot scarier than it is, I promise. Type this in, and hit Enter:
You will see a lot of text, most of it confusing. Look for "Ethernet adapter Local Area Connection", or "Ethernet adapter Local Area Connection 2" or similar. You will see a lot of lines indented underneath that. Look for an entry that says "IP Address", and write that down next to that computer's picture on your network map. Note: the computers in your network will all have IP addresses similar to your router. So, if your router's IP address is 192.168.1.1, your computers will be 192.168.1.100 (or similar). Do this for all the computers in your network map.
If you have wireless computers in the house, follow the above "ipconfig /all" instructions, but look for the entry that says "Ethernet adapter Wireless Network Connection", and write down the IP address you see there.
You have mapped your home network! Keep this map handy, and modify it whenever you add or remove computers from your network. It will come in handy for troubleshooting, I promise.
We're finally ready to troubleshoot your network. Most likely, you have one or more computers that can't access the internet. In our analogy, this means those plants aren't getting water. What we have to do here is see where the water's getting blocked up.
To do this, take a look at your network map. Your computer is connected to the router, which is connected to the modem, which is connected to whomever you're paying your internet bill to. We start at the computer, and work our way out.
Follow these steps to make sure your computer isn't the weak link in the chain here.
1. Make sure all cables are plugged in properly. Cat5 cables should insert with an audible "click".
2. Make sure the connection isn't disabled. Go to Start, then Control Panel, then double-click "Network Connections". Right-click on your connection and see if the top menu item says "Enable". If so, click on it--your connection was disabled!
If the above items aren't the problem, you should check to see if your computer is communicating with the router properly: Go to Start then "Run" and type in: cmd
Find your router's IP address from your network map, and type this in:
Replace "192.168.x.x" with your router's IP address, of course.
You should get four lines returned to you that start with "Reply from...". If you don't, then your computer is the problem or your router is turned off. How you proceed from here depends on what kind of computer or router you own. See your manuals for details, or call a friend who knows about these things.
If your computer can see the router, then (returning to our "garden" analogy) the water's flowing fine between the pump and the plants. Next step is to see if the water's being blocked from the filter to the pump: let's see if your router can see the modem. In the command window, type this:
As before, you should get four lines starting with "Reply from...". If not, then your modem's not talking to the outside world like it should. Call your internet provider and ask them if they can see your modem from their network. If they can't, then they will (or should) stay on the line to figure out the problem and get it fixed.
If they can see your modem, then you may have a bad (or unplugged) cat5 cable between your router and modem. You may also have a bad (or unplugged) coaxial cable (or phone line for DSL) between the modem and the wall plate.
It might be someting as simple as the modem needing a reboot, which your ISP can walk you through easily. Note that you may have to unplug the power from your router when you reboot the modem. Your ISP will tell you if you need to do this or not.
Hopefully, you've been able to restore internet connection to one or more computers on your home network. If not, the problem is a little more involved than the steps above have covered, and you may need to get some assistance from a friend or professional.