iTunes won't let me change my titles

Do you mean it's auto-completing your entries when you type them in? You can't turn it off, but you can work around it — instead of typing "KING", type "*KING" (or something similar), then delete the asterisk.

I've had some similar problem with some mp3 I got.

Dunno if yours is the same, but what I had was that when I changed the name of a song, artist, album or any field for that matter, from let's say "Pink Flooyd" to "Pink Floyd", when I played the song it changed again to "Pink Flooyd"... what I had to do is to re-convert those songs to mp3, they were already on mp3 format but anyways I selected them and clicked on Convert to mp3 and the new copy I got was ok. I do the same thing everytime I have an mp3 file with such problem and always work for me.

Yep, it works fine with Get Info. iTunes is capitalization-blind, in a sense. If you're trying to type in "abcdefg" and you already have "ABC123" in your library, iTunes will watch you type the first three letters and say, "Aha! She must be trying to type in ABC123 again!" It "suggests" ABC123, which means it's just capitalized your lower-case abc. You can finish typing the rest of the field, but the suggestion has already been made, so you'll wind up with ABCdefg.

You can get around this by not letting iTunes suggest anything. If iTunes sees a garbage character at the beginning that doesn't match anything else in its library, it won't have any suggestions to make. "Asterisk? Nothing starts with an asterisk — I have no idea what you're trying to type." This should work anywhere you enter data.

Did you check to see if the files are 'Locked'?

Open one of the folders in iTunes (HD>Music>iTunes>iTunes Music) with one of the difficult tracks. Click on 'Get Info'

At the bottom of the 'General' info there is a tick-box with 'Locked' next to it. If it is active (ticked) click on it to unlock it.