I have a sonoff 4ch pro since one year and a half and always worked fine. There were some problems with wifi connection but with new firmwares this was solved. But since a couple of days the sonoff directly does not work. All lights are off and if I unplug the power supply and plug again, the blue light turn on for about 5 seconds and then it turn off and the device do nothing. No button responds and the device seems to be dead. The device worked with DC but I tried it with AC and it does not work either. Firmware version is 2.7.1. Any idea?