2001 Ford Focus What's Wrong with the car?

I've had many problems with my car since I had it. Earlier this year my car rocked back and forth when it was idle. I took it to Pep Boys, where they did diagnositic and they said to replace the spark plugs. The light came back on and they said change the wires. The light kept coming back on a couple of times and finally stopped after changing both wires and plugs twice. Now my car won't start. When I tried to start the engine I thought I turned the key too fast and the car would shake, so I turned it off. The day it broke down on me, the car start shaking again so I let it roll a little to see if movement would make it stop and it cut itself off. Someone tried to jump it and there was a loud metal grinding noise. Since my car has been sitting around I try to start it and the metal grinding is gone but it still won't start. Someone told me that only one of the spark plugs is firing. What is going on?