she wont start

[MB61YAM]

having returned to riding after a 2 week ban (for major dental trauma) the old girl refused to start, connected the Optimate back up, just pressed the starter again and it fired up no problem, it fired up ok when I had filled it up 20 mins later, so could this be a faulty Optimate (it showed all lights lit up and the green was on) or could it be a battery which is borderline, it is five years old and has done a great deal of running, any thoughts guys ??