Sometimes, when I poke at a chip with my probe, a pin might be neither high nor low. It's just... dead. I can kind of understand how an input pin might read dead (based on the state of the circuit leading to that pin) but why would an output pin on something like a 7408 or 7402 read anything but low at the very least?

I'm working on a Firepower right now, and IC7 (which is a 7408 quad AND gate) has:

No signal at all on pin 4 (Input A)
A long-low-short-high pulse on Pin 5 (Input B)
No signal on pin 6 (The Output Pin)

Pin 4 is connected to Pin 19 of PIA 4 (the Solenoid PIA). Why would that line not give a reading? And why would the output pin also be dead? Should that at least be low, since one of its two input pins is dead?

I guess what I'm wondering is this. Of all the states a logic probe is presented as possibly being in, "no lights or sound at all" isn't one of them. Under what circumstances is would a logic probe legitimately show no activity whatsoever?