Can't get on the Internet? Can't print to network printer? It's bound to happen sooner or later. Wired Ethernet networks are pretty reliable, wireless ones can be brutally finicky. But no matter what type you're using, it's good to be prepared for networking failures in the future.
When there is a networking problem, the knee jerk reaction may be that there is something wrong with the computer. Perfectly understandable.
But the first step in debugging a networking problem should not involve any of the computers. Rather, you should look at the lights on the box(es) sitting at the hub of the network. The hardware is talking to you and may have something useful to say.
The box(es) may be a number of things. Often there is a broadband modem (cable or DSL) and a separate router. There may even be a third box for VOIP to which a normal telephone is connected. On the other hand, all these functions may be combined in a single box. The advice is the same either way.
Before trouble strikes look at the box(es) holding your network together and make a note of the normal state of every light while the network is functioning properly. Is the light on or off? Green or Amber? Solid or blinking?
So that it's always at hand, I suggest keeping this cheat sheet right next to the device in question. Maybe even tape it to the box, so it can't get lost. Now, when the network fails, the first thing to check is the lights on the box(es).
That's step one. Step two is to examine each box and make a note of the vendor and model number. Then go online to learn what every light can tell you. It's one thing to know that a certain light is normally green, but exactly what does it mean when the light is amber? Or blinking green instead of solid green?
I try to find the manual for the device at the web site of the hardware manufacturer. In addition, I try to find documentation on the lights at the website of the broadband provider. Cable and DSL modems can be modified by an ISP, so their documentation may be more accurate than that from the hardware manufacturer.
If you were given a manual/booklet/pamphlet with the device and can still find it, great. But this would be my last choice for information as it may not be up to date, may cover multiple models or may not reflect customizations made by the ISP.
If, at your ISP's web site, you can't find anything documenting the meaning of each light, then contact your ISP and ask them. Someday, you may be very thankful you did.