no start spark on one cylinder

[latkins09]

So I was driving today and my car was running fine and when I turned off the car and tried to start it again it wouldn't start checked the spark plugs by putting them on the valve cover and only one cylinder had spark this is on my 98 gsx , changed the transistor and still no start. It cranks fine and timing marks on top. Are lined up . Prior to turning the car off it idled and drove perfectly

 

[DSM1G90]

Laying the plugs on the head isn't the best way, where the plugs really needed to be clamped down on ground to really ensure definite connection. Coil issues if only one plug is firing.