Windows 8.1 Activation!

so i bought a new Dell Inspiron 3521 laptop with windows 8.1 and i am not able to activate it!
i tried the 'Activate Online' option which was of no use and i cant find the key anywhere! (i did not receive it)
and also i have used an app to locate my key and i tried entering it but that also dint work!
i am spending hours on this now!
please help!