Yesterday the computer tech forced the machine into sleep mode, but nothing happened afterwards. However... after you mentioned it a couple of posts ago, I forced it into sleep mode again and left it there for a few minutes, before reviving it. Now all of a sudden the screensaver works!
Oh good. Maybe the computer got tired and just needed a bit more sleep than it got yesterday.
Hard to say what really put it to rights. Could have been a Registry value that just needed a nudge or something.
The other day, I manually put the computer to sleep. Then I remembered something I hadn't done and pressed the 'Enter' button to wake it up again. However, it hadn't quite finished putting itself to bed. Pressing the Enter button before this was done, completely upset the computer. It took a few reboots to sort it out. Computers can be touchy things.