If there is not enough charge in the battery it will not turn over fast enough to start. If you completely flattened the battery a 6 amp charge will probably take 2-3 days to fully charge it again. A bigger out put charger could 'cook' the battery so the lower and slower the better but, too low a charge will not work either The clicking is the relay kicking in and out, if you keep doing this it can damage the relay or even weld it's contacts together. Try a 2 or 3 day charge at 6 to 8 amps, or equivalent to half the capacity of the battery. This will be written on the battery some where. You could get a boost jump charge start, but again relays can get cooked.
Hope this helps.
In the extreme you could sit on the bike and get some one to push you up to 'running' speed and try bump starting it , use 2nd or 3rd gear not 1st. Have fun, bin there dun that!