So sometimes when i log onto my pc it asks me to activate the key even though i already have. Is it bug or what?
Open CMD as administrator and type in, without quotation marks, "smlgr -ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX" (XXXXX being your product key). Hit enter once you've done that and a notification should appear saying your product key has been successfully installed. Restart your computer and see if it still asks for activation. (This is based on you having a legitimate key in the first place).
But it's only once in a while it asks and i bought it in the local mall.
you could try the Phone activation.
i dont remember the exact procedure to get there in windows 8, but google is your friend :D