Sound in one ear?

Hello,
A few months ago when I upgraded my motherboard to a ASRock A790GXH/128M I experienced several problems with the onboard sound card. After installing the drivers, I could only hear out of the right ear of my headphones and out of the right speaker depending on which i plugged in. I noticed I could fix this problem by pulling the plug out slightly so that it's about half way in. This however wasn't a great solution for my so I finally gave up by installing an old sound card which fixed my problems. I recently reformatted and installed Vista instead of XP. Now I'm having the exact same problem but I cannot fix it because my old sound card does not have vista-compatible drivers. When I had asked this question before, most people agreed that this was a problem with the hardware and that I should try to replace it. This time however I installed linux over my vista installation and the linux audio drivers seemed to work perfectly. Strangely, after the linux installation my vista audio worked too. Linux was giving me problems and I decided to delete the partition and have only vista on my machine and the problem is back to where it was.

So to summarize:
- running vista ultimate 64-bit version
- motherboard: ASRock A790GXH/128M
- on board audio chipset: VIA VT1708S
- sound works only in right ear (with any speakers or headphones i use)
- sound works in both ears when plug is only inserted half way
- sound works in both ears with linux drivers on both OSes (when duel-booting which I am no longer doing)

Any idea on how to fix this? I know buying a new sound card would work but I would rather not spend money.

Thanks a lot!