Neither derailleur will work? What happens a LOT is bike builders don't leave enough slack in the wire at the shifter. People do all sorts of things when they ride or transport bikes. If you're attaching the strap in a way that could pull on the tape/wire that could be it. Has the bike gone down recently and then has the shifters straightened?
At the shop I would plug it into e-tube w/ the battery charger and see what the computer recognizes...that tells me a lot.