No sound - files transferred vista laptop to XP desktop

[jigsaws]

I use audacity for editing oral history recordings. I usually work on a desktop running XP.
However, recently I labelled a recording on a laptop running vista. This worked well - no trouble getting it to playback. I then transferred the audacity files from the recorder to a desktop. When I open the project I see the usual stereo tracks with traces and the label track, so the sound seems to be there and the files complete, but I can't get any sound when I click play. Audacity projects that were labelled on the XP desktop are fine.
The preferences, as I understand them, are characteristic of the machine not the files - anyway I can't see any difference between the various preference and/or system options when one or the other project is open.
I have put the files on a memory stick to make sure that I have everything I need on the XP desktop. When I open the project from the stick, I can playback the project with sound on the vista laptop, but still no sound on the XP desktop
The only difference I can see is that the input selector is greyed out in the files transferred from the laptop. As far as I can see this is not my problem, but I have hunted through the material about greyed out input selectors with no result.
What's going on?

[steve]

Audacity projects do not transport easily - read this article to understand why: http://audacityteam.org/wiki/index.php? ... ement_Tips