| Thanks Timeslip for your help (yes, I want to check the left/right alt keys individually) but I read in the MSDN Library this: 
 "... Although the least significant bit of the return value indicates whether the key has been pressed since the last query, due to the pre-emptive multitasking nature of Windows, another application can call GetAsyncKeyState and receive the "recently pressed" bit instead of your application..."
 
 From all these above I understand that if another application call GetAsyncKeyState() then my application will not respond...
 
 EDIT: I checked your suggestion and it works fine...
 
 
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