Hop aroma is gone!

Just tasted my Simcoe IPA last night. Two weeks in the keg. Crappy beer to say the least. Don't know what happened but there is one tell-tale sign. All the hop aroma is gone. Completely. Smelled great going into the keg. Now there is nothing. I force carbed. Could there be an issue with the CO2 that I got? I did get this from a welding supply place but didn't think there was a difference in CO2. Is there such a thing as "food grade" CO2?

How long was your primary, and how long did you dry hop? How much did you dry hop with?

One week in primary, one week in secondary with dry hops, 1.5 weeks in keg, force carbed at 12psi @ 34 degrees for ~48 hours. This is now the second IPA that has gone wrong on me via the kegging. Had an Irish Red in between that I bottled that was fine.