show us a picture of the h/u ik with mine u just pull apart the pieces and it pulls out but some need keys if it uses a metal cage others dont so lets see it

 

no that grounding point is fine as i've been using it since i got my setup like a year ago. put up a pic of your headunit and we should be able to tell you how to take it out

 

If the power and ground are ok as well as your amp and sub then your only left w/ the remote wire. Most headunits come w/ the tools you need to remove them and usually they are 2 thin metal shims that slide down the side of the headunit. It's possible the remote output on the headunit went bad I have seen it happen before.

 

Are sure the amp coils aren't fried? I mean its pretty damn hard to fry an amp but not impossible on an Alpine. A friend of mine had the exact same symptoms. The amp would turn on but no power to the sub. Dunno just an idea.