How have you got on with resolving the non-start issue?
Any more clues as to why it is not firing up?
If the battery is charged and the plugs are new then I assume that checks have been done to see that a spark is present.
Then the only other thing is fuel supply. Sometimes fuel goes stale when a car is left parked for a period of time but 3 months is not that long in the scale of things.
One other option to check out is that there is no rodent damage to wiring while it has been in the garage as this can be a common cause with cars being laid up over the winter