Bose SoundDock Series II power light flashes but no sound

I recently bought a Bose SoundDock Series II at a thrift store for cheap because it was missing its power cable. I bought a power cable on eBay and plugged it in. The green power light on the front of the machine flashes briefly but there are no beeps or any sound at all from the speakers. I replaced the sound processor board next, but it hasn’t made any difference. Any ideas what to check next?