I once was asked to look at a friend's mum's PC. He said it had got to the stage where it took twenty minutes to start and then crawled along with all kinds off windows opening on their own. It had been on-line for about 3 years with no AV, firewall or anti spy/mal. It had never been de-fragged, msconfiged etc. I ressurected it with the usual spring clean type stuff, whereupon he told me that mum didn't 'trust it' anymore, had bought a £1000 laptop and I could keep the PC "as it was never any good anyway". It's upstairs hooked up to a steering wheel and pedals for the kids (and me) to play games on.