Won't beep at all...
Most ESCs (including BLHeli firmware) have some beeps when they get powered up, regardless of what signal they are getting. If the signal is "normal motor off" you get normal startup beeps. If the signal is "full throttle" you get ESC calibration beeps (followed by programming beeps for some brands of firmware). If the signal is in between, you get crazy klaxon error beeps. If there is no signal at all, you get a lost model beep.
So I would start by measuring the voltage going into the ESC at the thick battery leads.
Some "Opto ESCs" actually require receiving 5v power over the servo connector.
There was a version of BLHeli and a version of LP that did not like each other, and there are reports that it would finally beep and arm many minutes (1-15?) later. You may try that and try searching the forum (and maybe even the wiki) for that.