Entertainment Center: TVs, Stereos, VCRs and DVDs - Receiver popping off ???

Hello, I hope I can get some good advise about a problem I am having with my Pioneer multi-channel receiver model VSX-D608. For more than six years, I have had no problems with it and the Bose 5.1 speakers connected to it. Then, just recently, after a lightning storm (Florida), the receiver will power off and on continuously, if the volume is set to –19db or louder. A loud pop is heard on the center speaker, and then the receiver powers off for about 5 seconds. When it powers back on, it immediately pops and powers off, then continues the cycle. If I reduce the volume to –20db through –99db, it works fine. But if set to –19 or more, it will not stay on. Initially, after the lightning storm, only the right front and left front speakers worked (but still would pop off at –19db or more). After re-programming, they all work (but still pop off at –19 or more). Any ideas what could be the problem? I checked the speaker wires, and there are no breaks or shorts.