what amp is it ? You can first do a quick test ..
1: ..Turn system off ...
2: Unhook speakers ...
3: Turn system on ..
4: Check amp to see if protect light us still on ....
5: Turn system back off before rail voltage climbs from no speakers detected ....
6: If protect light was still on bad amp ....throw amp away .....if protect light was off a bad speaker .... find bad speaker and replace