You're not alone.
Last summer, we got a seriously well paid rock trio gig. (For us anyway) We would play for 40 mins and get €1,000 between us. PA supplied as per our requirements but no engineer. We got a mate in to mix us and set about setting up the PA as it had been delivered but just dumped on the stage.
6 foldback monitors, 4 FOH cabs. Huge desk and huge power amp.
Nothing, not a sound.
After 40 minutes of head scratching, panic and trying to get in touch with the sound hire company, a member of the future audience says "shouldn't those two big fat cables be plugged in somewhere?" We had nothing coming out of the power amps.
Durrr.