I re-booted and decided to log in as a different user to see if Control Panel and program removal would be functional under another profile. It said something about br_funcs.exe (0XC000142) function failed something and then closed. I plugged a mouse in to request that the machine shut down again. I re-booted and it got to the log-in screen but my cursor was inoperative (this happens a LOT with both of my Lenovo T61s so I don't know if it is just a Lenovo quirk). In the end I had to long-press the physical computer power button. I then tried to turn off the machine but couldn't get it to switch off even when I asked via Task Manager. I wanted to select the Silverlight plug-in from there to get rid of it. Control Panel was very slow and then I couldn't get the list of installed programs to display. Later on, when the Firefox browser was getting unresponsive and complaining about Silverlight, I decided I would try to uninstall that plug-in. A second try let me and I thought it was a temporary glith and that everything was OK. I had some initial trouble with that computer yesterday when I couldn't get Control Panel to display anything when I wanted to install a program. The drive that has shown this is connected to the XP machine that you were helping me with recently. I have read that Windows will put them on all drives if you haven't instructed it not to. I don't know why there is a System Volume on the drive.

System volume information virus