Timing light not picking up spark

[Scott26]

I know i have a dead cylinder on #5 . I got my timing light to test if it had spark to it and it only lights up about every 5 seconds. all the other cylinders light up normal.if the plug is fowled or carbon bridged will that stop the timing light from lighting up??or is it from the distributor. So if the timing light does not pick up spark or light up does that mean its a distributor problem or from the spark plug not working?.