@jbke89 It's a TTL output from the Nano so the voltages should be low (<~0.8V) or high (>~2.5V), but since it's a PWM signal you will get varied measurements using a volt meter. Using an oscilloscope you would see the levels and modulated square wave output.
In this case it sounds like your output is always low but the laser is always on, likely a pull down resistor would fix that but the real problem is why it doesn't turn on. Are you getting the Grbl connect string? If not, your Nano needs to be flashed.