No sound in edit view

Well, the settings in edit view and mutitrack view are not, unfortunately, the same... you can set them the same, but it's not that way by default.
I haven't used 1.5 in a while, but my initial guess is that one of these are true:

1. You've muted audio play-back on the edit view
2. You've disabled monitoring on edit view
3. The playback source in edit view is set to the wrong hardware.
4. I believe there was a playback volume controle even in 1.5.  If so, you could have actually turned the volume all the way down for playback..

If I get a chance later this afternoon, I might try reinstalling 1.5 and seeing if I can get figure it out on that version.
Post back with your results so far.
Also, it'll be helpful to know what version of Windows you're using.  In Windows Vista, there's a volume mixer where you can control the volume for any open applications as well as Windows sounds - different than the typical mixer setup in XP and prior.