Wordpress title tag

I noticed that a lot of themes somehow override <title> tag. I want platinumseo to handle it but wordpress just won't let it do that. I tried editing <title> tag in header.php, even removing it, but title still stays the same (whatever i set the blog title in wordpress settings). I'm starting to get a headache from this crap. Can anyone help me?

If editing title in header.php doesnt give result then some plugin is overriding your title tag

Does your header.php change (like your title returns back in it or it stays the same once you delete things there?)