Strange Sound


When I start up, I hear a whirring sound coming from within, and it will stay on the screen with the apple.
It seems to happen when I leave my computer on overnight. Like, it won't work for a couple days, then it will work, but I leave it on, and I'll get this problem where I'm stuck on the start up screen.
When the computer does work, it only works for a few minutes, then I hear the sound I described, and it'll be stuck.