Something which I have done for a few years now and which has saved my bacon on not a few occasions, is the keeping of a journal where I write all the information pertinent to the PC, including all the changes to my PC hardware, software etc, documenting the whole process of trying to fix things and so on. Its also being recommended by Jack Schofield in this article yesterday's Guardian (UK national newspaper).
You won't believe the number of times I have had to refer back to it to remember how I fixed a problem the last time round, or seek out an infrequently used password. Its also something that doesn't tend to stop working even when your PC has fallen on its face.