I have a 2009 mb pro and several days ago I got a warning that my startup disk was almost full. I deleted hundreds of videos and pictures I no longer needed, freeing up about 43 gb after emptying trash. Now I am getting the same warning again and it is telling me i only have 900 mb left! How is this possible?! I haven't downloaded anything or used the computer heavily since then. I have deleted basically everything except the bare bones and it still isn't freeing anything up. Help??