I've had my Sony STR-DE415 for about 10 years without a problem--recently it developed one. After turning it on, the display flashes "protect" and I get no sound. I no longer have the manual, so I'm not sure what this means or how to fix it. I've checked all the wiring and it appears to be in order--speaker cables are properly connect at both ends, as is the stereo cable from my CD player (also a Sony). Anyone know what's up? Thanks.