Usb crashes after i turn off external synth

Im having issues with my usb ports,
I have an external synth Nord a1r which connects via usb, everything works fine on startup and it connects once i turn the unit on from the power switch on the back. The problem comes after i disconnect the synth then come back to it and try to reconnect nothing happens. All the usb ports that are still connected work fine, its anything new i add like a i phone or printer nothing happens until i restart.
This only happens once i have used Cubase.

I have removed the old drivers, deleted all the drivers and reinstalled them. Done a fresh install. still the same.
Also when i come to restart it just hangs on the shutting down part then bsod after about 10 mins. This only happens if i turn on my external synth.

im using windows 7, 64bit, cubase 7 Please help im going crazy!!!

any ideas will be gratfully recieved.