'95 Blazer Won't Start!!!

I've had this blazer sitting for no more than 4 months. It started fine 4 months ago w/o a problem, I had a surpentine belt snap on me & its been awhile since I could get around to getting one and putting it on. Today, I put on the belt and went to start the blazer, Nothing, Dead silence. So i got a new battery thinking, maybe its the battery and if not at least ill have a extra battery lying around. Switched out the batteries and still Nothing, Dead silence. I thought that if it were the starter it would at least try to turn over, maybe im wrong. and also if it were the alternator wouldn't you been able to jump it to start it it just wouldn't be able to keep charge?? Im not exactly car smart but if i get a head start on what could be the problem, i know i can get it started, if someone could just give me some possiblities and let me know what would be the easiest way to tell if my starter or alternator is bad. Thanks

Use a volt meter and check the voltage on the battery. If over 12 volt does the headlights turn on. Check the voltage at the starter is it 12 volts.
With the vehicle on jack stands use the voltage meter and check if the little wire going to the solenoid is getting 12 volts when somebody is trying to start the vehicle. If it is I would suggest a rebuilt starter and solenoid.