Cannot connect 2 mp3 players to computer

Question

I have a sansa260 4 gig and a diamond dsm967-1g player and when I hook them both to my computer running Win XP Home Ed. My computer only shows one or the other depending which one I hook first. Any Ideas? Also I get a message saying my device has malfunctioned and I should replace it....They work fine independently when hooked to my computer....Maybe I should replace windows instead he he