Audio seems to power off my set

So I was given a Sanyo 42" television (DP42840) by a friend who isn't tech savvy, claiming that it powers off.

Upon trying it myself, I would attempt to turn it on, see the power on light turn on, and then turn off after several seconds. On occasion I would be able to turn it on, but if I turned it off, it would go back to not wanting to power on.

After opening the unit up, I checked around but didn't find anything like bulging capacitors or anything like that.

Recently I replaced the backlight inverter board since I could hear a wine coming from mine (reconditioned, less than $10).

Not sure if that did anything or not, but now the set works... if I don't continue to play sound through it.

I've hooked up my surround sound Blu ray system to it, and it works great (the HDMI cable doesn't send any sound to the set, all sound goes to the systems' speakers).

I've hooked up my Xbox 360 to the same HDMI input, and the TV promptly shuts down after a few seconds.

Today I hooked up my laptop to it: it works, as long as I don't hook up computer sound (in fact, after hooking up the sound, just by sending the Windows dining sound through it, the TV shuts down).

So as far as I can tell, if the Sanyo TV at least receives audio, it cuts out.

Any suggestions?

I am a technician, so soldering isn't a problem. Thanks!