1. Actually, there’s no way to download windows update using IDM, windows will start the official downloads when the internet is connected automatically and will install when the computer is SWITCHED OFF (see comments for a different explanation)
2. Sir, you have a delicate problem, the product key is written in the DVD box of your WIN 8 OS, so go and ask the SHOP you bought your LAPTOP for the DVD BOX,
If they give you the BOX enter the product key, and install it genuinely
If not then download this activator for installing the WIN 8 OS as genuine, it is trustworthy software & virus-free. so to download click below.