Starting Up

I have a 1999 Chevy Prizm. It does not want to start. Some times it will start but not on its own power, I have to connect it to a battery charger or jump the car. The starter,battery,spark plugs are fine. The altornator is only like 5 months old. When I turn the key some times it does nothing and some times it clicks and some times I can her the started turn. Any body know???? Could it be the strater selonoid???