Could be a failing hard disk. Find out your hard drive's maker and model and download the diagnostic utilities from their site. This tutorial
tells you what to do to find out what hard drive you have (among other things).
As for the "disk 0", that's normal. Machines start to count with 0, not with 1 like humans do. So if you have 3 devices, for a machine you will have "device 0", "device 1" and "device 2".