No sound ARRRGH!

W7 32bit home. This morning I changed out the PS in my office box. (replaced with the original 300w). reconnected everything and wham, no sound on speakers.
I dual boot with XP Home on another drive. Sound works. I conclude all the connections are fine.
Realtek HD Audio. Drivers up to date. Since I'm in the mood for concluding, I assume it's a setting that has gotten out of whack.
I use this computer to pipe music to my home stereo and that's not working (obviously).
Check Audio Center or whatever it's called and see that my choices for speakers are Stereo, Quad, or 5.1 Surround. Mine are 2.1 but there is no option for that but okay, I seem to recall this from the original setup. I try to be thorough and while testing in quad, sound comes out from my speakers but only the ones that are supposed to be behind me
I'm sure I've missed something simple here but....
Any suggestions?

Re-install the latest driver. Unless you installed it very recently, consider it a version update anyway. This driver is brand new:

http://www.realtek.com/downloads/dow...&GetDown=false

Thanks TG

I have version 6.0.1.5963. I downloaded 6.1.1 and Windows refused to install it. I uninstalled 6.01 and then went to properties and Windows started a troubleshooting session and 6.0.1 was reinstalled. I have sound now. Interesting because I tried this troubleshooting session earlier in the day and nothing was resolved.

Thanks for the suggestion and helping nudge this thing in the right direction.