Can't Sign in to my apple ID...

Well 2 days back my iphone started showing sign in to your apple ID after starting any of my applications..the problem is that after entering my email and password the windows disappears and nothing happens. I tried signing in from settings, but that also didn't work. after entering my email and password, It says could not sign in, there was a problem connecting to the server. This is the first time a problem like this is happening. I also tried changing my password but that also didn't solve the problem. I did a full reset on my iphone but still no solution. What should I do?