My iPhone 4s has always connected to home Wi-Fi but suddenly stopped?

I've had my iPhone 4s for almost two years and it has always connected to my home Wi-Fi. However, about 2 days ago it stopped connecting and whenever I try to connect it says "unable to join the network". I know it's not my router because all laptops are working and my dad's iPhone 5 and brother's iPhone 4s connect automatically without any issues. Any suggestions on how to fix this?

Someone in your house change The router password you need change it on your iPhone as well so you can connect to your Wi-Fi again.