QUOTE (odyssey @ Nov 3 2009, 17:53)

Verify your output. if you restored an old foobar2000 installation it probably points to a non-existent output device. Eventually try different output-modes.
I think I had a similar problems with some output modes in Windows 7, which didn't really make sense to me, but I just switched to others that worked flawlessly. Could be driver-related.
I had the same problem a few times. It didn't want to play any file in the list. It has nothing to do with any previous installations since I always make a clean installment of this beautiful piece of software. Also, the OS version doesn't have anything to do with it because I've had XP Professional, 7 and now Vista SP1. It must be a flaw in the source code somewhere.
Your indication, however, made me solve the problem : File -> Preferences (CTRL+P) -> Playback -> Output -> Output Device (where i selected the specific hardware audio device).
Thank you, it saved me a reinstall and a couple of tweaks.