retina macbook pro can’t auto connect to wifi after wifi router rebooted

My macbook pro with retina can’t automatically connect to wifi after the wifi router was rebooted. There is exclamation mark on wifi sign. As I clicked the wifi sign, it shows no Internet connects. However, It is strange there is a tick in front of my wifi name. In order to use wifi, I had to click off wifi, and then click on. The previous version, Macbook pro, has no problem like this. I had deleted all files under wifi library, but still fail. Appreciating for any way to solve it!