apple id and icloud

every time i unlock my phone it asks me to enter my apple id password. i enter the CORRECT password it just asks me to enter the password again. it keeps repeating this until i am forced to just not enter the password at all. this then doesn't allow me to use an features of my phone. when i go to sign out of my iCloud my phone freezes and doesn't let me sign out. also if i go to reset my iPhone to factory settings whenever i press the reset button my phone again freezes and it doesn't let me do this. i am also unable to connect to the internet therefore unable to update my iPhone. when i attempt to connect my phone to iTunes it gives me a pop up error message saying "iTunes could not connect to this iPhone. An unknown error has occurred (0xE8000015)". if i attempt to connect any other devices to itunes on my computer it works fine apart from this device. i cant use my phone or seem to be able to do anything at all to fix it.

[Edited by Moderator]