WiFi, Internet problems, possible solutions

WiFi and Internet problems are hard to diagnose and usually rare, so this is my known list of possible causes /solutions seen here on the forums / experience

This is a work in progress, run through them and see if any of them work or apply to you.

On for some time, then just kicks one off / won't connect

You have a DCHP "lease" which allows a machine to be on a certain amount of time with the router.

Check the time and date are correct in your computers System Preferences and that it's being updated with Apple's time servers.

Check with Airport Utility that there is a update that needs to be applied to the Airport's firmware.

Also run your Software Update fully for OS X too.

If that doesn't work, try this:

Go to your System Preference > Network > Airport > Advanced > Airport and use the "-" button to delete all your saved network connections.

Reboot the machine, and manually connect in the upper right hand corner and when it ask "save to keychain" do that.

Another way is to change your routers network name and/or security features, connect manually in the upper right hand corner and when it asks to save in KeyChain, do so.

Won't connect after wake from sleep, reboot, or coming back into range

If you have a "hidden network" it doesn't broadcast a SSID, the Mac will only ask if it's there upon a reboot or manual connection. Not upon a wake up from sleep or if it gets out of range of the Wifi.

To stop this you need to unhide your network, hidden networks and MAC address filtering offer no protection against hackers.

 Info- discussions.apple.com