Activate windows 7 online check box

Hey everyone, i was curious about when doing a clean install of windows on an OEM machine, (using a disc burned iso image). should you insert the COA sticker key and leave the checkbox of automatically activate windows 7 while online box? I heard that may not work. Or should you just leave the box checked and not insert a key? I have also been told to not check that box at all. I know about backing up activation and what not, but im asking in a hypthetical situation if windows would not boot at all. What would you do to activate an OEM machine? It all has me bit confused whether you need to insert a key AND check that box, or you can insert a key without checking the box and vice versa. Any help is appreciated

Thankyou!

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