Hello, I've a big problem. When I tried to start my macbook air this morning it made the normal startup sound followed by the grey apple logo. But after that the computer showed me for just a few seconds that my startup disk is full followed by a blue screen. My desktop disappeared and I can't see or open my programs any more. Only a few programs that open automatically when I start my macbook appear. I can't delete things to clean up the startup disk. Does anybody knows what to do?