Blackscreen

Hello, so i have a big problem i my win 7 toshiba computer and when i started it then after bios(basic input output system) then everything went black then i rebooted it and enterd bios and choose my usb that has win 7 and then i loaded files then went black again but the mouse appeared and i shut the computer down and started i tryed to press f8 rapidly and it didint work pleese help