Hi Jenny100 - And thanks for responding so quickly
I've checked out my programmes that run at start-up but don't appear to have any of those that are mentioned in the link you gave as possibly causing problems.
Nor do I use a cordless mouse.
And the only thing that has been changed recently
is the adjusting of settings on my router to allow me to use WiFi stuff.
I've never bothered with any WiFi gadjets and so never bothered with the wireless settings of my Router - but I was recently gifted an iPad and so yesterday my Son in Law came round and dealt with the Router settings for me.
But would that affect screensavers on my PC ??