Apple ID won't work, not able to use any services, and it says can't verify server

A notification box keeps popping up asking me to put in my Apple ID password, but after I do, it doesn't accept it and keeps popping up. It also says I'm connected to a server pretending to be an "iCloud server" that can damage confidential information. It also says "can't verify server" whenever I attempt to open an app. I've reset my password, and turned on/off my phone many times, but it's still messed up. Please help!