in 1 tb i installed 8.1 ,os windows 7 in 37 gb .while starting my pc error called (an operating system wasn't found.try disconnecting.only driver they don't contain an operating system y press ctrl+alt+del) but i'll press f11 will restart and asks drive to select while selecting 1 tb it won't works but in 31 gb it works what will be the reason . why 1 tb is not getting booted by starting stage it's acting like a simple driive that i can copy paste and have . why 1 tb is not booting without an other hard disk (37 gb)