[Q] USB debugging not working

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http://forum.xda-developers.com – I have been trying to root my htc evo 3d for virgin moblie. While I was trying to unlock the bootloader the deives drivers wont instal while usb debugging is on. If It's off I can access my sd on my computer but if USB debugging is on my computer says that the device drivers could not instal. I have tried useing Htc sync to get the drivers but that didn't work. (HowTos)