Firing Issues????

Seems like? A good start would be to go get a spark tester and be positive you have no spark. Do you have a set of noid lights to check if the injectors are firing as well? If its backfiring, you should be getting spark or you wouldnt have any backfire at all.

When did this start? Did you do anything or did anything happen that made this start?

If you can narrow it down and say that you DO have spark, fuel and compression, then technically it should start. If you dont have one of those, then you know where your problem is. If you have all 3 and it still wont run, then you probably have some type of timing/signal issue either in the crank or the cam position sensors.