Laptop won't boot up windows without going into bios

My computer has started doing this bizarre thing where it boots to an black screen with an cursor in the corner. i have to press f12 and select hard drive, once i get to windows boot up screen, its fine, i have run Alien autopsy and it says everything okay. its driving me crazy, i know what to do if its black screening after the alien head logo, adn if windows boots to black screen. Can someone aid me?