But if i may cut in, sounds very like a problem i had with my old cinq, have you tried using a different battery? I tried all sorts of stuff right down to changing the starter motor (got couple of spare ones for a 899 if any1 needs one, PM me). In the end it was the battery, it still read 12volts on a tester, but was just old and knackered.
Just borrow any battery to test, if it works go buy new battery.