A clicking sound indicates either flat battery, a bad connection on the battery, or a starter motor. All are possible after sitting for an extended period. You need a proper diagnosis. Do the headlights come on? If you have them on and try to start it, do they go dim?

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue