Windows 7 - Audio right channel not working at all after installing windows 7

Hi guys!

First i want to apologize for my bad english since i'm italian

So.. I just installed windows7 ultimate and suddenly the right audio channel is not working.

1) I want to make clear i've tried different cables and headphones/speakers (i'm a producer so i've got plenty..) and i can't hear the right channel at all.

2) I tried to download latest version of Realtek and it didn't help

3) On audio configuration when i press the configure button and it starts helping me configuring it, when i tried the right audio channel i could hear it very low (like the left channel is at least 10 times higher). that is the only situation in wich i can hear something coming out from my right speaker (and is like a 90w monitor.. so i think i'll hear it otherwise)

4) Since i just installed everything i tried to format and re-install, but i got no results

5) I tried the bit/hz thing but with ANY configuration i don't get any result

6) And now a very odd thing: since i got an external audio interface i tried even with that. right channel still not working.

Aaaaaaaaaaaand now some hardware things that may be helpfull to help me (hopefull)

DualCore AMD Athlon 64 X2, 2500 MHz (12.5 x 200) 4800+
2gb RAM ddr2
MB: Asus M2N-MX SE Plus
OS: Windows 7 Ultimate
Audio Interface: nVIDIA nForce 6100-430 (MCP61P) - High Definition Audio Controller PCI (RealTek ALC662)

Did i forget anything?

I really hope someone could help me since i'm stuck with my producing work (i don't want to work in mono or with just a channel )

Thank you in advance

Update: now with the external audio interface is working on both channels in stereo

Now i wonder why without this isn't working fine on right channel.. :/