need to install windows 7 home premium oa

Hello.

I just had to replace the HDD in my dell latitude e6520 laptop. the previously one was malfunctioning.

I was trying to download windows 7 from microsoft site with the original key but its showing

" The product key you've entered appears to be for software which was pre-installed by the device manufacturer. Please contact the device manufacturer for software recovery options." 

And I am unable to download / install it.

Is there any way I can download win7 home premium oa that i bought with my laptop?

Thanks