I was playing a show last Friday night with my passive P Bass running into the passive input on my Hartke LH500 head, then into an Acoustic B410 cab. In the last song I heard a massive buzzing noise come from my amp. The sound cut out but then almost instantly came back. For the next few days the amp worked, but with a constant high-pitched squeal that worsened when I switched on the tweeter. Today I plugged in the head into the Acoustic B410 and there was almost no sound at all. Only a very quiet signal when the amp was cranked. I also plugged the head into my other cab (Avatar B410) and there was the same problem. I tried the active input on the head and it works just fine. What could my problem be and what would be the best way to fix it?