The router was 5 years old and was a TalkTalk issue Siemens Gigaset. My PC was off and I was listening to an album on my media player's HDD (ie I wasn't streaming so the router was effectively not in use). All of a sudden there was a short 'parp' noise from the loudspeakers and the router's lights went out.

Luckily, I had a spare. Can anyone suggest what could have caused the old router to blow?