Why isn't the Wi-Fi on my iPhone 4 working, even though the signal is strong?

It worked this morning. It worked when I went out for lunch (Starbucks has free Wi-Fi, duh.). And it worked when I went shopping (at Target.
However, when I came back home around late afternoon it stopped working. I have Wi-Fi in my house, and even when the signal is strong, it just keep loading it. No usual checkmark that shows it works. The Wi-Fi works fine on my brother's 3DS and we already checked the home computer router. I just don't know what's wrong.

The profile might be corrupt. Try to remove it and let it reconnect.

-> Go to Settings
-> Wi-Fi
-> click on the arrow to the right of your networks name
-> Forget network
-> Back to Wi-Fi
-> click on your network name
-> write in password.ok

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