A green light alone isn't necessarily meaningful, but suspect your amp could be the issue. Can you get it to work if you bypass the auto-on switch?
From the photograph, that amp is class D with a switching power supply. The power supply has failed. They are notoriously difficult to trouble shoot and very expensive to sort out. It is not worth it.
I can not even find a user manual and not even any published specs. I have found the odd review and it was not well thought of. It only has a 9" driver and as far as I can tell was part of some sort of glorified HTIB. It is a 17 year old sub, and subs have improved a lot since then. Apparently it did not produce much bass, according to many reviews. They are well known for the problem you describe.
The bottom line is that unit is junk and needs a fast track to the recycling center. It is not even worth fitting a generic plate amp to the unit.
The bottom line is that you had a boat anchor dumped on you.