Hi John,
Not sure what type of computer and operating system you are using but assuming all that end is good, i would suggest, if you have not already, take it one step at a time.
The easiest one I think would be the mixer. Make sure you have installed the drivers for the mixer on your laptop. Now connect the USB from your mixer to your laptop. the utility for the DJM 900 should pop up after doing this (don't worry about Traktor until you do this first).
If this doesn't work for you, change USB ports on the laptop. if possible, if you're still out of luck, try a different PC or laptop (don't forget to install drivers and always download fresh; don't use the file you have not had luck with just to be safe. Do this regardless of your usb ports reading thumb drives or not. It's important to rule one thing out at a time to get to the bottom of this.
Post back and by then, someone will surly help out...
Good luck
