Unknown problem

  infiniti/fx-3545/2003-2008

Hello Everyone, i have a 2005 fx35 infinity which was shaking a little when on red light, so i went to a mechanic shop and they told me it was coil #3 so i went to auto zone and purchase a spark plug,and the coil, went on and change it and Boom it crank perfect no shaking at all, 30 minutes later i was on my way home started loosing power so i parked it and, cut it off, now it only cranks but wont Start, no lights in the dash all normal, just wont start. What could it be?

 

6