Nothing could be further from the truth...
.. I'm very grateful for all your comments and suggestions.
Having been promised by the shop where I bought the computer that somebody would be here at 8.30 this morning, I've been waiting all day for the guy to arrive. Looks like I'll have to wait another day - oh, the joys of living in SE Asia!
I was hoping to be able to post later today how it got sorted out, but alas.......
I definitely will report back once they've taken a look at it.
Strangely enough, it hasn't crashed yet yesterday or today.
And there's one more symptom: now and again when I enter text with the keyboard, nothing happens immediately and there is a delay of a few seconds before the typed text appears on the screen. Could this also be a memory-related problem perhaps?