after reinstall windows product key not valid for activation

So after a motherboard failure i replace it and reinstall windows with the same key i had with this system before but now i get the product key is not valid for activation. I have tried the SLUI.exe 4 to activate via phone but it just brings me strait to the not valid page asking me to buy new or change. Cant seem to figure this one out. Any help would be appreciated. As a side note i try to...