On the early +4s you turn on the ignition with a key , but starting is via a button which is separate.
If you do not even hear a starter solenoid clicking, it may be the battery, it may be the solenoid, it could be the battery earth, and it could also be the starter motor, or the engine earth.
If it ran OK a couple of days ago , unless you have left some lights on and drained it , it is rather unlikely to be the battery, but worth checking anyway. I rather suspect other causes.
I would operate the solenoid manually and if that brings nothing, check the battery earth (and feed) terminals and the earth to chassis connection which must be good. I would also check the engine earth strap , and again both connections need to be clean , bright, and well fixed.
It is possible that the starter has jammed , although it does seem unlikely as I think the solenoid should click if this were the case, so rock the car backwards and forwards whilst in gear to free it off, then try again.
