The issue here is that you are creating a new Lock (KeyGuardLock) every time the "if" statement executes. You can disable a lock the first time when you create it but you must "reenable" the lock which you disabled in the first place, you cannot create a new one.
The solution is to make the lock outside of the onClickListener. i.e. Take the following code out of the "if" statement and declare it before setting the onClickListener:-
KeyguardManager myKeyGuard = (KeyguardManager) getSystemService(Context.KEYGUARD_SERVICE);
KeyguardLock myLock = myKeyGuard
.newKeyguardLock(KEYGUARD_SERVICE);