Set the Initial State of the Particle emitter to Disabled. Then OnCollision with that ballThing, Move the Particle emitter to Player.X/Y and set Particle emitter to Enabled.
I just recreated the particles with the name deathExplosion2 and gave it the exact same events and it started working again? Something weird going on here, I have had this happen to a few projects where I don't even touch them for days and come back and something is not working and if I just recreate the object with the exact same events then it works again, this must be some kind of bug, not sure whats going on here.
Also the way you suggested you said set the emiiter to Disabled, I see no option in properties to toggle the state of the emitter, do you mean change say the Rate to 0 then set it on collision?