well.. before you buy a new one, go play somebody else's and see if it sounds the same. try some out at guitar shops and see if you still have the same problem. because i'm not sure if buying a new guitar's gonna solve your problem.

a picture of your guitar or a recording or something could help.

for all we know the problem could be with your amp. turn the amp off and play and see if when you play smoke on the water, it doesn't sound like the wrong notes, like it does with the amp on.