#1
So I just bought Ibanze GRG270 with a edge-III tremolo on. I can tune it and the bridge float perfectly. After locking the nut, the tuning is still correct. But after I use the whammy bar everything just go out of tune. So frustating. My shoulder hurt from tuning too much but still can't get it in tune. Help would be nice  
#2
It's likely that you're having issues with your locking nut. You may not have it locked correctly, you may not have it locked tight enough, or (if the guitar was used) it may be worn. Make sure the locking clamps are going the right direction and that you've used the proper wrench to lock the strings down. If they move back and forth in the nut, you're screwed.

If you've just changed strings, there are some additional possibilities. You may not have the strings locked in the bridge saddles correctly, or the strings are stretching (new ones do that for a while).

What are you doing with your shoulder that involves tuning? Once the lock nut is locked down, you do NOT use the headstock tuners any more, You realize that, right? You have to loosen the locking nut (with the wrench...you do use a wrench, right? Finger tight won't work) and THEN tune, then lock down the nut again.

One suggestion: unscrew the fine tuners about 3/4 of the way. Sometimes when you clamp the locking nut the strings will go slightly sharp, and you'll have to unscrew the fine tuners slightly to get things tuned again correctly, but after that, in almost every instance that you have to use the fine tuners, the strings will have stretched a bit and gone flat.
#3
Tune the guitar up then lock it. Once that is done try turning the tuning peg (on the headstock but not too much or you will snap the string between the headstock and nut) if the pitch changes then its the nut if not then its possibly the knife edges.
#5
dspellman m33sta Thanks for your reply.

So I think the problem is the nut, I didn't lock it tight enough. But I watched a video and the guy said something about don't tight the nut too tight or it would embed the sting into the nut, thus need to change the locking nut. I don't remember but it's something like that. Thanks again!!!!!