Hello again,
I am not confident pulling it apart, so may pay for expert help.
It is a Dell Inspiron 1545, less than 2 years old.
To re-cap, does not start up, no screen, after about two minutes of switching on, it emits the beeps, in groups of 4, ie 1 beep, 2 beep, 3beep, 4 beep, small gap...