How did you not have a fuse on the amp's power wire from that battery? No offense, that is plain idiotic. You would have saved yourself the grief.
Did you check the battery voltage? A test light won't tell you much. You should be using a multimeter.
Is your amp's power wire wired directly to the battery? If so, I would think your battery is fried.
Sponsored by Momentum BMW #593...We Bleed BMW BLUE