Hello Essexboy.
Have '50 times' uninstalled and reinstalled Java's latest update, with no positive result.
In the meantime have erased here and there all references to Java...
As I realized the last Firefox update (3.6 v.) probably wouldn't function (saw something about it on Java page), have returned to version 3.5.7 .
Today have reinstalled many times the Java last version and tried to install U16 v. and U5 v. (I had the '.exe' files somewhere in my PC).
Tired of trying I decided to run the oldest version (U5) and to see if it worked (is the only version which Java page recognizes as installed in the PC). Blocked the last version plugins in Firefox ... and tried to see the video I was trying to watch days ago...
To my surprise: It functions now! : I can watch the video OK.
The only problem is that Java keeps asking to update to the last version...

(Thank you again for your help and patience Essexboy

)
Hope all goes OK...
On the other side, I cannot enter the DOS desktop yet... (and I think there stays the solution to freely update Java...)
What about the clock, please?
(I still have to change the hour each time I turn on the PC.)