my 1996 Tahoe wont start when i turn the key i hear a clicking noise as i do turn the key and i see a small drain from the voltmeter. this has happened once before and that time i put it in neutral and it started right up i tryed to do the same again but no luck. the truck also has been hard starting for the past month instead of its normal instant start up and rev. any one have any idea on what might be wrong