Nothing from speaker/headphone jack

I've been using my AO751h for a couple of months now and it's been great. I'm sold. However, recently I tried to watch a movie, plugged my phones into the green "sound out" jack and nothing. The sound continued to come from the onboard speakers. Does anyone know if this is a hardware problem or some simple setting that I may have missed. I've checked all the usual settings, but all to no avail. I can return it from whence it came but that's gonna be a pain in itself. I was considering doing a factory reset, but again, a real pain to get my apps back. I don't use the machine for permanent storage so file backup is not so much of a problem. I also created a Ghost image as soon as I had got my apps added and rid the hard drive of the usual rubbish. Any input would be greatly appreciated.