Everything- it won't turn on. I was able to do some experiments, and right now it seems to be the combination of two things- a defective contact with the power button (which I can't fumble my way to), and my hard disk, which seems to be broken, or at least it won't boot anymore. I've been able to connect it to another computer with an USB adapter, and it loads when the computer has booted. I was a bit pissy about it because that hard disk has all my uni stuff on it, but apparently I'll at least be able to do some backups there, but for a working computer it seems I need a new one.