Why won't my car start?

I have a 1995 Buick Park Avenue 6 cylinder with approx. 50m miles (I put in another motor that had 37,000 miles on it) and it won't start. My mechanic passed away last Friday and I really can never afford to put money into my car so I'm trying to avoid paying to have it towed and pay the cost of another mechanic I'm not familiar with so any diagnosis options I can get as to what might be the problem would help me greatly. I'm hoping someone is on right now that can answer me before I leave for work in a hour otherwise I will have to have it towed later on this morning. When I first tried to start it the other night and I turned on the ignition it was clicking. Then it stopped completely and there is now nothing. The battery cables are tight and there is a cylinder looking thing on the opposite side of the car that continues to making a funny clicking sound even after I've gotten out of the car. Any suggestions? Mechanic on the phone thinks starter?