Two days ago, when I came home from work, my computer, which had been left on all day, had a black screen which stated (from my memory, didn't write it down): Sorry for the inconvenience, there has been a change which prevents windows from starting. This was followed by several options to boot Windows. I tried every option: Boot normally, Boot Safe Mode, Last Known good. None of these options worked, so I tried to boot up from the Window XP CD which also didn't work. Then I tried using the recovery console to repair but found that chkdsk /r would start checking the drive but would hang up at 14% complete, which I let run for a couple hours but which appeared frozen at 14% complete. Next, I tried to perform an in place upgrade from the Windows XP CD. Before it upgrades it does a chkdsk which again hung up at 14% complete. I let this run about 8 hours but found it was frozen at 14% complete. I don't have a recent backup - my bad.
Back ground: the day before the XP boot up problem, I had used CCleaner to do a registry scan and clean. Could this have caused the problem?
Any ideas on what else I might try?