| Finally sussed it. My p.c has some in-built card readers,s.d ect, which are u.s.b devices. There must be some sort of conflict as when I disable them in Device manager then my p.c sees the mp3 ok. Device manager doesn't show any conflicts but tells me everything is working correctly.
Anybody know a long term fix for this other then disabling the card readers each time. | 
Threaded Mode