When I installed the windows 7 the partition with win8 was the first to boot. I think when you install a new OS it makes it default.I didnt do anything like that myself.
This error didnt occur at a videogame rather at logging off from win8 environment(after a game couldnt be tabbed into again,no graphic glitches of any kind and the card is like 2 months old)
tried the bcdedit and I cant find windows 8 anywhere there.If you mean I should enter it manually i didnt understand the "identifier number" part.
here is a screenshot of the command prompt
http://i.imgur.com/J5y1L.jpg