I tried all the start up stuff and nothing was found in the hijack log. 'CrustyOldBloke' gave me some more things to try but I was unable to reply because the symptoms got worse.
Yesterday I suddenly ceased to be able to use the keyboard. Guess what - tried another keyboard and all the symptoms disappeared! !
So thanks for all your help but it turns out my problem was just a faulty keyboard not a malicious virus!
Many thanks anyway - it great to know there are people like yourselves to turn to.