it's a very wide shot but often in old computers their backup battery gets weak. It doesn't show if you run them every day but after a longer pause you'll notice that the date and time settings are off.
Maybe your current problem is related? There might be some data loss in the settings or simply a difference in time/date between the devices that keeps them from communicating properly.
One of my old machines has that prob - when starting it, it insists that it's Jan 1st 1900 and won't accept files or devices that date at a later year since it's impossible (from the computer's point of view) that a file or device can come from the future. It works perfectly the moment I correct the time settings manually.