IOS 8 WIFI PROBLEM ?Unable to join the network?!!

I've updated my iPhone 5c to IOS 8 and I now can't connect to the internet. I've tried more than hundred timeshare from last night ,I'm getting crazy now !!

The WiFi is free in school and it has no passWord .

There had not any problem before I update to the IOS 8 last night .

sudenly my iPhone 5 gives this message "Unable to Join the network ..." when i try to join my WiFi at school (My dormitory mate has no problem with IOS 7.1.2 and also with same iPhone ,same version also ).My laptop can connect to the WiFi very easily .I've tried to reboot my device, restart my router, on & off the airplane mode, reset network settings, and everything I found in discussion with common topic, but nothing's work.

please help me !!