If a roll of film comes out blank, or has only the faintest traces of images, the first thing to look for is the edge print. Don't give any other evidence or memory of how the film was exposed any consideration until you've examined the edge print.
The edge print is exposed onto the film during manufacture. It develops like a normal image. If is is not present or just as weak as the faint traces of images then the fault lies solely in the processing. If it developed completly, dark black numbers and text on negatives or clean white or slightly yellow on slides, then processing was reasonably correct and the problem lies elsewhere.
What does the edge print look like??