Led lights and usb ports work screen is blank

Hello, i have had a problem for a while now where my computer will sometimes turn on fully. Sometimes it wont turn on and the video card fan takes a bit to start then spins insanely fast making a loud noise and does not boot. durning this time all the led lights and usb ports are working fine but i am not getting any display and the screen is blank. Any idea to as what this could be is greatly appreciated.