Disc boot failure insert system disc after nearly 3 years.?

Ok so almost 3 years ago I built a computer, and it has worked fine ever since. I turned off my computer before i went to bed last night and this morning i couldn't boot up. Both my HDD still register in my bios as being connected but only one has windows installed the other is just all my files, could this be a dead hard drive(hopefully not as I don't have a windows key anymore) or could it be an error that i can correct?