Ok, from the beginning.

I bought a mexican Fender Telecaster from a shop last November (2008). It was on sale cheap because it had been stored in a warehouse that had been hit badly by rain and it had gotten a bit wet, but because it hadn't been there long I thought this wouldn't affect it and it'd be good as new.

So as it goes, all is perfect (and seriously, no problems with the electronics or anything), until suddenly the first string goes apeshit and won't stay in tune. But that is the only problem, all the other strings are fine, which leads me to believe that maybe the neck has bent a bit, and if I change it it should go back to how it should be?

Any help would be very welcome, and if it's good news even better, saves me a lot of money on a new guitar, xD

Thanks in advance, and sorry again if I've got the wrong category.

Note: when I say it won't stay in tune, what I mean is I tune it normally, and open string it's an E, as normal, but then it'll get to the 5th fret and it's Am, and on the 12th its D#.

Once again, thank you.
sounds like intonation problems, have you intonated it properly yet?
Quote by Scowmoo

You deserved this, Matt.
Forgot to mention, yes, I've adjusted it and still the same problem. All the other strings are perfect, except for the first string, which tunes itself to a perfect Em on the twelfth. xDxD
does it sound right?
if it aint intonation idk what it is.

and if its only one string... thats totaly wack... O_o
Quote by Scowmoo

You deserved this, Matt.
I've heard of wacky intonation problems happening with old strings..

if you've got it intonated properly, and if you can't see any warps in the neck, just try changing the string. it could be as simple as that.