on my Squier strat,the 19th,20th,and 21st frets all sound the same,it didnt used to do this,it hs always played fine,does anyone know why this is happening?
perpaps the frets are worn away?

do you get any sting buzz from around that area?
Your neck might be warped, and another possiblility is that your 21st fret is rising up, its nothing you did to it if the fret is coming up, it happened to my friends guitar, but his jsut buzzed the 11th and 12th frets, take it to a guitar shop theyll figure out wahts up, if its still under warranty itll be really cheap if not free.
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There may be a few things going on. The string may not be straight, and may have a bend that rests on the 21st fret, which means that when you push on the 19th and 20th the string is pressed down in two places, and obviously the higher place is gonna produce the note. If you have a whammy bar, press down on it to relax the strings, and check for any odd bends in the string

The 21st fret may be too high, if the 19th or 20th fret has been worn down it may be lower than the 21st, meaning the string is always going to rest on it. This may be the problem if the strings are fine.

Try changing the strings and see if the problems still there. If it is you may need 2 get someone to fix it professionally, or just get a new guitar

hope this helped
if that was to my post then you could refret the neck, although that would be quite a tough job, or you could purhcase a new neck, or purchase a new guitar? :\
Mine did the same thing!
I have a blue squire and I think i solved that by using new strings and adjusting my bridge.
It might just be a fret that is slightly off