I'm somewhat of a battery expert as I have a few cars and garden machinery that lie unused for months!
Two things I'd say. Most of the time, once a battery is flat, it's as good as dead. There's little point recharging them as sooner or later it's going to let you down. Some will disagree and sometimes a new battery can be brought to life - but usually a fully depleted battery will have damaged cells and won't hold a charge.
Secondly, it sounds like you've lost the required 'woof' or Cranking Amps in your battery. So it will be enough to power lights and things, but not quite enough to turn over the engine - so the starter clicks. You can quite cheaply buy a CCA tester which will give you the available amperage.
As above, clean (rough up) the earthing just to be certain its not that - then try a jump start and you'll find that hopefully your starter is just fine.... Buy yourself a new battery.
