Are the negs totally opaque, or totally transparent?
If it's totally opaque, it was exposed to a bright light source prior to developing (like the film was pulled out of the canister in a bright room).
If it's totally transparent with NO rebates, it means that somehow or another, all the emulsion has been dissolved away.
If it's totally transparent with the rebate intact, the film was not exposed at all (film not loaded properly, winding mechanism didn't work, lens cap was on or mistakenly sent in a brand new roll of film for developing).