The Power of PPrune never ceases to amaze...
Thanks everyone - all your advice gratefully accepted and tried...
Connected the errant machine to friend's monitor and everything OK...
Disconnected and still the same problem - everything works fine until the Sign-On Box appears, when suddenly the screen goes 'black' half way through typing in user name...Typing 'in the dark' so to speak, after user name and password have been entered, the screen flickers back to life for a less than a second before disappearing again...
All very strange to a TechnoDinosaur like myself...
Will download everything to the HD back-up as quickly as possible using the monitor, and then 'fiddle' around with the settings - if its a hardware problem, then no chance of me fixing it as I can't really manage much more than checking the tyre pressure on Frau H's car as far as engineering goes...
Thanks again...