48K WAVs won't

I am working on a remix and the stems I've been given are 48kHz and 32bit (I usually work with projects at 44.1 and 24bit)

When I import these files the waveform display for all of them looks like digital noise. So I've tried a number of things :

- converted the files to 44.1 and 24 bit. When I do this the files appear ok in the Sample Editor and on the arrange page (ie i can see the waveforms appropriately displayed). However when I play the song, though the playhead moves as normal there is no sound output. And when I try to play the files from the Sample Editor the playhead won't move at all.

- converted the project to 48kHz. Same deal. WAVS won't display correctly until I manually convert them. But then, no sound...even though they appear normal.

These files all play fine from the desktop using Quicktime.

Does anyone know what the problem might be?

Cheers

(Using LOGIC 9.1.4 and MOTU 828 and Snow Leopard)