Why does my wireless network keep disconnecting?
You may find that you have been disconnected from a wireless network even though you wanted to stay connected. Your computer will normally try to reconnect to the network as soon as this happens (the network icon on the menu bar will pulse if it is trying to reconnect), but it can be annoying, especially if you were using the internet at the time.
Weak wireless signal
A common reason for being disconnected from a wireless network is that you have low signal. Wireless networks have a limited range, so if you are too far away from the wireless base station you may not be able to get a strong enough signal to maintain a connection. Walls and other objects between you and the base station can also weaken the signal.
The network icon on the menu bar displays how strong your wireless signal is. If the signal looks low, try moving closer to the wireless base station.
Network connection not being established properly
Sometimes, when you connect to a wireless network, it may appear that you have successfully connected at first, but then you will be disconnected soon after. This normally happens because your computer was only partially successful in connecting to the network - it managed to establish a connection, but was unable to finalize the connection for some reason and so was disconnected.
A possible reason for this is that you entered the wrong wireless passphrase, or that your computer was not allowed on the network (because the network requires a username to log in, for example).
Unreliable wireless hardware/drivers
Some wireless network hardware can be a little unreliable. Wireless networks are complicated, so wireless cards and base stations occasionally run into minor problems and may drop connections. This is annoying, but it happens quite regularly with many devices. If you are disconnected from wireless connections from time to time, this may be the only reason. If it happens very regularly, you may want to consider getting some different hardware.
Busy wireless networks
Wireless networks in busy places (in universities and coffee shops, for example) often have many computers trying to connect to them at once. Sometimes these networks get too busy and may not be able to handle all of the computers that are trying to connect, so some of them get disconnected.