hi,
you say it wont even turn over??? so i assume you mean wont crank on the starter motor when you turn the key? if thats the case then its nothing to do with plugs,software or mass meter you need to be looking at immobilizer problems or if the immobilizer light goes out and doesnt flash etc.. then starter connections or even starter relay problems,fuses etc...

if the car cranks over but doesnt fire up then yes you need to go back and check what you have done since it last ran e.g. are the plug coils connected up and are the leads on the right way around, is the mass meter plugged in correctly etc.. if your dealer did an upgrade the car must have run afterwards or they would not have given it back to you so i dont see how the upgrade could be a part of your problem.

steve.