I do not have Google+, I do not have 2 step verification, and I have no data to show in my data tools tab online. So, why do I keep getting an error message that my password is incorrect or my account has changed? I didn't change anything, in fact, I never use it. Have I been hacked? If so, how can I resolve this so it doesn't keep happening?
First try what Izzy suggested in his comment. If that doesnt help then..
Log out of all Google apps, then...
sign in through appropriate app or..
try to sign in through your browser
If neither will work then remove your Google account from your device and re-add your account. Remember to back up your device prior to doing this, otherwise your contacts, messages, and few other things will be deleted. PlayStore and everything else will be fine.
You might have a connection error after adding your account while validating your info, if so go into your YouTube app and login that way.
That is how I fixed the problem on my device. I was able to sign right in.