Since the blinking light occurs immediately when the unit is turned on, this is an indication that the protection circuit has detected a fault. Usually this means that either the speaker wires are crossed (shorted together somewhere) or that the output section itself has failed. To verify this, disconnect the speaker wires from the receiver and try again. If the same thing happens, then the internal transistor output stage has failed and requires service.
Please note that any of the speaker output channels can trigger this problem. If you have a diode checking meter, you can check the outputs yourself. Replace any that are shorted and replace both transistors in a channel you find shorted as they work in tandem even if only one tests bad.
Dan