Try to unplug battery, charger and RAM and CMOS battery, keep the power button pressed for 20 seconds, plug ONLY charger and see if it beeps, with no RAM installed it should beep. Seems similar as an no-post issue I think.
I've encountered this issue with all the iPhones I've had. It's an iOS issue, I think it can't stream 2 audio streams at a time. Swipe to open control center and play the music. Then turn off the sound in the game using game options.