DJM 750mk2 HID problem

Hi, 

I have just bought and am running:

2 x CDJ 900 nexus

DJM 750mk 2

rekordbox 5

all the kit is connected to my laptop with the USB printer type cable.

I have watched countless videos on the subject, and I managed to ket the laptop to recognise and control the CDJs with little difficulty, however no matter what preferences/settings i change in rekordbox and how much i randomly fiddle with inputs and other knobs and dials on the mixer. i can't get it to make any noise. I can play cds fine, and my turntables work fine. i am sure i am missing something obvious, but any pointers/solutions would be great.

oh, one final thing (and this is probably the reason), i can't get the 750 drivers to install no matter what i do (have reinstalled rekordbox and drivers etc) and i have tried fixes suggested elsewhere on this forum.

thanks in advance for your help!