You need to determine whether No 5 cylinder has a spark or not, pulling off the plug lead and it making no difference could be due to other reasons not necessarily just a missing spark.
Have you actually made sure there is a spark arriving at No 5 cylinder by removing the lead from the plug,fitting a known good plug into the lead,grounding the plug body and then getting someone to crank the engine overwhile you look to see if a spark is being produced.
The other possible causes of a misfire on one cylinder is a faulty fuel injector for that cylinder (swop it with another one and see if the fault moves confirming a faulty injector) also check the injector wiring as well is it trapped or damaged?
Lastly and the most unlikely is a lack of cylinder compression on No5, unlikely but not impossible!