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#11
I can only think of two possible explanations for why you cannot connect.
You may be typing the password incorrectly without realising it. Double check that you are using the correct password. If you are absolutely sure it's the right one, then maybe you keyboard has accidentally been switched to use a different language layout. Or perhaps Cap Lock is turned on. Another possibility is that is you have a small keybord without a separate numeric keypad, then Num Lock may be turned on. If so you may not be typing all the characters exactly as you think you are typing them. After you've typed it, but before clicking on 'Connect', click on the little icon that looks like an eye at the right hand end of the password box. This will show you the text that you have typed instead of just a series of dots.
It's possible that the WiFi card in the laptop has developed a fault. This seems unlikely though, if you can see your router's name in the list available networks and it asks for a password when you try to connect then it would appear to still be working.