PC communication problem?
My SX3 sometimes has a hissy fit at turn on, and I think is due to a watchdog problem.
Anyway, after turning on X4, and Mach3 not communicating, unplug parallel cable, hit Mach3 RESET (big red on screen) and plug in cable.
Hit the reset again, and you shouldn't get a negative looking status message.
Switch X4 from local to remote.
If all this is to no avail, the break out board where the parallel cable connects to may have a loose connection.
Check that the wires from the power transformer to the BOB are not frayed or loose.
Although Frans would have checked all screwed and crimped connections, these are the first places you should check.
If the machine is working in manual mode, everything after the BOB should be OK. I think it supplies power to some other areas too.
LED states on drivers vary depending on the microstepping position. See the Driver PDF (syil.cn) for explanation of LED states. Documentations is OK.
Hissing noises are not abnormal, with these switchmode supplies, when lightly loaded, as when E-S is active.
If the machine JOGS, look for PC/Mach3/Cable problems.
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.