New Amp (green light on) no sound

I recently hooked up my Amp and went to test it tonight with a old sub I have. I know the sub works because we tested it on another amp this week.

Amp turns on, but no sound from the sub. Checked the amp ground, power and remote power, all good.

I have a double din with a dedicated sub in, I put one of the RCAs (white) in there and plugged into the amp, tried a y cable both from the amp and HU and still no sound.

So I was thinking it has to be a bad amp, or a bad RCA cable? Also, if the ground was bad would the amp still turn on?

 

Do you have a multimeter? If not, might be worth it to get one to check if any voltage is coming out of the amp (speakers), and going into the amp (RCAs). Have you checked that the amp gain setting hasn't been reduced to 0, does the amp have a fuse? Personally, I would first check the amp voltages in and out (speaker out and RCAs in), check that you have 12v going to the amp, and recheck the ground.