why our GMC Sierra pickup truck won't start?

[Lori]

We have replaced the starter, battery, ignition switch, ignition key switch and the pick-up still will not start.
We have replaced the battery, ignition switch, ignition key switch and 2 starters. Its a 1990 GMC Sierra. It will not start.

 

[rpdm]

clicks - won't start

2000 Savana 2500 5.7L 3/4 ton - also replaced same items and relay, clicks but won't start. Cleaned connections of corrosion. Lately has needed 'jumped' in the mornings. Then wouldn't last all day so tried to find out why.

 

[mmaextreme]

Somethings draining the battery, have you checked the altenator to see if its functioning properly?