Dell — Slow process and didn't find ms office product key

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Hyderabad, Andhra Pradesh

I brought a new dell vostro 3546 i5(5th Gen) laptop on 07 aug 2015. which is having 4GB RAM and 4GB(2GB+2GB NVIDIA) Graph card. although i didn't spend much time with it but the system getting slow. and to activate ms office it is asking product key. I want to know how to over come those problems.. where should I get the ms office product key. pleasereaply as early as possible.