It deleted everything in my inventory, chests, hoppers, droppers, dispensers, and item frames.

I'm guessing you opened the world in the snapshot, then in the 1.7.4 version. See MC-45009 - going backwards in versions is NOT supported, and in any case when using snapshots the system specifically says to make backups as there is no guarantee against (possibly world-destroying) bugs.

ya, I did.

Please to not create two tickets about the same issue like MC-48253