I don't know what it is, it just doesn't sound well, even though the tunner says it is correctly tuned. It was working alright like an hour ago and now when I want to play it just sounds bad. I really have no idea what could have happened. Help please?

Thanks you

Okey people, I already figured out. It was not the string which was wrong, but the tuner. After retuning it myself the ol' style it sounds alright now. However it still disgusts me that it went out of tune so suddenly. Whatever.