ABOSULUTELY STRANGE. Just returned from the surrounding hills and used only MF. On return uploaded images to PC and also deleted the upgrade file from the card.
When I read MattMatic's post, I found that the focus ring was actually moving, focusing, I guess. But, much more, it actually focuses and activates the shutter. What a surprise when I saw properly focused images on my review.

Guess, the Czech mountain gremlins have left..... it seems to be working fine...
so, what's left? Just to say many thanks to all of you for your suggestions. Really appreciated, particularly so far from home. That's the advantage of the wide web, I guess...

Have successfully upgraded, using the pdf instructions. Very clear guide, must say...idiot proof, to boot...
Now, I can use the AF.S option, but ONLY in the Preview mode. I have to focus manually. If not in Preview, it still purrrrrs along.
Any ideas?

Just to confirm to Johnx: when in AF.S and AF.C, the focus drive PROTRUDES, when in MF, it is FLUSH. Which is correct.
will do the upgarde today, using Anvh's pdf. The upgrade came with a readme.txt file.
will let you know what happens.

anvh: have left the battery out for some four hours. Still purrs. So I think I should do the update?

MattMatic: Try pressing the "AF" button on the back of the K20D. If it makes the same noise when you press just the AF button then it's a focus issue
(Normally the camera will auto focus when you half-press the shutter, but this can be adjusted in the custom menus)

As I said, you are right. It makes the same noise..what adjustment could I try before going through the update?

Any ideas on this, before I update?

Alfpics:have no blower, so will do as JohnX suggests. Have specially charged battery for the purpose. And will move the fle outside the DMIC folder.
If it all explodes, so be it... the World has to come to an end somehow... will let you know when done...

MattMatic: have checked the pins after having left the battery out for about an hour. The pins work as you said: When in AF.S and AF.C, the focus driver retracts. In MF, it is flush with the body.
When in AF.S it makes same purring noise as when I press the AF button on the back of the body.
Now the shutter works in AF.C and MF...
What next guys? Oh, btw, thanks for all the comments and suggestions, seems that I am getting there slowly, in the mountains of North Czech Republic....

polchraine: will do as suggested. Have had a look at the pins. When I press the lens locating pin, the focus drive does not budge. Btw, what is'pinging'?

JohnX: Have obtained the firm update software. The file is FWD183B. Have copied it to the root of the DCIM folder on the card and confirmed that it is at DCIM/FWD183B.
The readme file that came with the update told me to turn on the power whilst pressing the Menu button. When I do this, only the version number, which is 1, appears. It does not say 'loading'. just displays the version number and after a second or two goes to the usual menu items. No updating request is displayed?
What should I do to achieve the task, please?
As I am out of the UK, cannot look up my manuals.

alfpics:have cleaned the conacts, still the same. Could this have happened when I changed the lens from 18-55 to 50-200 and back again? I don't hear the familiar click when the lens is docked home. They both work OK in manual focus and in AF.C, although only one frame is taken. In either mode it does not auto focus. Not sure, but have noticed that when I press the shutter button, the Flash sign blinks on and off, with the A icon on when in all the modes, AF.S, AF.C and MF. Maybe there all the time, but have not noticed it before. Have reset the custom settings and now get 'All the custom functions values are by default' and a little square appears in the LCD panel, left corner, next to the flash and the A icon, which is always on. As I am away from the UK, cannot refer to by books.. Have not done the upgrade, as had to fully charge the battery, as suggested elsewhere. Have checked and have Version 1.0..