Please try the following:

If you have Photoshop 6, try turning off image previews. You can do this via edit > preferences > saving files > image previews = Never Save

If that is not effective please try the following. From within PowerDesk right-click on any image file (e.g., a jpg file) go to > properties > Photoshop Image tab > Uncheck Generate Thumbnails. This should restore the speed of file list display.