In reply to er658497...
Are you being interupted while turning the wheel during the harpoon event? During that event you have a limited time to perform the necessary rotations to defeat the boss. If you are being interupted, they "may" reset the count or cause enough of a delay to make the fight seem impossible. This is performed more easily in coop as one person can defend the other while they turn the wheel. I realize that's little consulation if you are attempting to beat the game without going into coop however.