Quick check... If the amp still stays in safety mode with the vol turned down and the speakers disconnected, it will have failed in some way. Since you have the safety operation light ON, you can expect that the power transformer is OK. I would expect that you have a DC offset condition on one channel. The most common problems you may have are
- dry solder joints about the power stages such as regulators, and output/driver transistors/IC's.
- blown output transistors/output IC with possible fusible resistor failures, and or sometimes burnt up printed circuit tracks.
- a voltage rail failure from a burnt fusible or power supply component.
If you are up with electronic fault finding, soldering and have the tools, have a go yourself, I could talk you through it. If not, I would suggest you contact you local HiFi specialist and find who can repair it or at least check to see what has failed for you. Good Luck. If you cannot find someone, hit me back and I will try to find someone for you. Cheers