have you carried out a compression test on the two cylinders that are not firing?

also try taking out one of the spark plugs that are not firing and put the ht lead back onto it, then touch the spark plug onto the body of the car, you should get a nice fat spark on the plug, if not your problem is on the elctrical side of things.are there any other dodgy symptoms? car runs hot, water in the oil,smoke out the exhaust etc?