The past week I've been having this problem, and it's becoming more frequent.
Sometimes I turn the car on and the Pioneer boots up and I can hear the sound just fine... but occasionally (last week it was about once a day) it would boot up, but have NO SOUND at all.
Today I turned the car on in the morning, and it was fine. When I left for lunch, there was NO SOUND coming out. I tried turning it off and on again, same thing. Then when I came back from lunch, again, NO SOUND.
WTF is going on?!? 
Basic information needed here.
What kind of car, is there a amplifier and are they stock or aftermarket speakers.
Usually it's a shorted out speaker, which results in shutting down all the sound on the deck to prevent damage.
2008 Corvette - with Bose system
Stock speakers
Using the Pioneer-Bose adapter
Pioneer does not make a Bose adaptor. I would look into the module if anything.
I'm not sure on the 2008, but previous years the remote turn on drew alot of current in those cars. A relay on the remote wire would fix that.
pin 85 to rem wire on deck, pin 86 to ground, 87 to constant and 30 to remote wire going into the module, 87a not used.
i had something similar to this. i had an alpine system with a power acoustik capacitor. one day the capacitor died and whenever a hard hitting bass occured in the song the sub would turn off. because the cap wasnt working to regulate the current whenever it drew alot of power the sub shut it self off....now u have a 12v radio powering speakers that normally work on 5.5v with no adaptor. could be the problem right there... but heres an adaptor for you to try it out
i had something similar to this. i had an alpine system with a power acoustik capacitor. one day the capacitor died and whenever a hard hitting bass occured in the song the sub would turn off. because the cap wasnt working to regulate the current whenever it drew alot of power the sub shut it self off....now u have a 12v radio powering speakers that normally work on 5.5v with no adaptor. could be the problem right there... but heres an adaptor for you to try it out
That's the adapter I have.
I would try the relay as suggested above then.
Another option would be just to try a metra gmos-04 mdule, found at any best buy or circuit city. It's cheaper, and can be returned easily if it does not solve the issue.
happended to me, amplifier was makin the proper connection
one of my speakers would turn on and off randomly. i looked at the bose adapter and retightened all the speaker wires and havent had a problem since.
I also have a 2008 Corvette and am experiencing the same issue. Have you tried any of the remedies mentioned here? Have you found a resolution to the problem?
Thanks..