Thanks gavinzach for the suggestion. I have now checked every key on the keyboard and they all work as expected (except the Insert function of course - there is MS Support tech solution for that but I do not want to have overwrite function.)
I have removed SecureDoc boot login screen and also decrypted the whole disk to eliminate that as a source of problem - no change.
I have also accessed Win tools (Ctrl Alt Del on start-up brought up boot options repair etc. I ran boot repair twice and no fault found but not solved the long beep on start-up.
The password still fills with chars when I come to Win login. Backspace them and enter password works.
Is there any possibility that there is a software problem that generates chars like a stuck key?
Is there any utility that I can run to test k/bd?