... hit the power button- it's in Control Panel => System => Advanced. In the Startup and Recovery Settings, untick Automatically Restart. Thanks Paul. More information arising. I withdraw my suggestion that this is a hardware reset fault. But it still looks to me to be a hardware problem rather than software. I changed that setting, and then found that I could do quite a bit of close zooming around 1 pixel per full screen, zooming in and out and even closer, until eventually I saw this: 2_111515_480000000.png I then had a hunch that it might simply be the graphics chip overheating, so I waited a few minutes for it to cool, and then clicked OK. Sure enough it carried on working fine. I could zoom back out and the entire computer appeared normal. I was able to make the above screenshot in the usual way. I then did a restart as instructed above, but I saw no blue screens and no error messages. This was with an 8-bit (grey-scale) bitmap at 300dpi ...