Setting up your modem wrong can cause problems with your Internet connection.

Keep these best practices in mind:

Despite faster speeds reaching most homes around the globe, wireless (and often wired) networks can get bogged down. If your Internet connection is still working but the speeds are slower than normal, there is usually a logical explanation that can usually be fixed.

Cause: The most obvious problem with Wi-Fi speeds slowing down is being too far from the router. The further you are from the router, the more unreliable the connection and its throughput will become.

Fix: To fix this, just get a little closer. If the router is located in a different room, try going into the room where the router is located and see if that fixes the issue. If this is a consistent issue, try to position your router higher (up on a shelf), away from other devices, which can interfere with it, and in a central location in your home.

If that doesn't work, consider purchasing a second router and a set of powerline network adapters to extend your network.

If you can't connect to the Internet at all, the first thing you should do is take a look at your router's LED status indicators. If there are no lights at all, the router is probably unplugged or powered down. Disconnect the power cord and reconnect it after a minute or two. Make sure that the Power switch is in the On position. If the router still isn't powering up, you may have a failed power adapter, a faulty power strip, or a fried router.

Reconnect

Check Your Status

If the Power LED is lit, check the Internet or WAN indicator. On most routers, this should be green and may be flashing. If your router doesn't have status indicators, look around back to see if the Ethernet port lights are flashing. If there is no activity, turn the router off. Unplug and reconnect each cable, making sure each cable is seated correctly in the appropriate port. Wait a few minutes before rebooting the router. If you still can't connect to the Internet, try the next step.

Cable Connection Okay? 

Before you start thinking about resetting or replacing your router, inspect the cable connection coming into your home. This is usually located on the side of your house and may or may not be housed in an enclosure. Make sure that the main cable hasn't been chewed up by a squirrel or knocked loose by debris from a storm. If a cable splitter is being used, make sure each connection is tight and the connectors are properly crimped. If the splitter looks suspect (i.e., rusty or dirty), try replacing it.
Start Fresh 

If rebooting your router doesn't do the trick, try resetting it to its factory defaults and performing a fresh install. For most routers, this is done by pressing a very small reset button on the rear panel and holding it down for several seconds until the LED lights begin flashing. Once reset, use the accompanying disk or Web-based setup utility to reinstall the router.

If you can connect to the Internet, but the connection drops or is slow, consider these recommendations.

If you lose your Internet connection when you use your landline phone, you may have a problem with the way your phone and modem are setup. Your phone line carries two signals -- one voice and one data. In order for both to share the same line without interrupting each other, the equipment in your home has to be set up correctly. Read Using filters and How to properly connect a landline phone through the same wall phone jack as the modem to learn more. You might also look at What to do if your Internet connection drops frequently.