I never had this problem before.  I'm using X2, Win 7-64.
I haven't changed any settings in preferences recently.  Maybe I am overlooking something?
All my wav files are on a separate hard drive.
When I open a new project the wavs auto play like they are supposed to in the browser.
However after a couple hours of work, adding audio tracks mostly, they no longer play.
I can see the stop button light up, like the file is playing, but I cant hear anything....Weird!
Also, when I drag the files to and audio track they also play fine.  Just not the browser Auto-Play.

Any Ideas?

Okay.......I think it's because of the other HD.
I have all my samples on F:  a 75 GB HD that only has about 6 GB free on it.

When I navigate back to C: and click on a Wav, it plays in the browser.
So for whatever reason, I think it's because the drive is almost full because they were working before.