PC can't recognize the mps2+ usb

The document said that PC should now recognize the motherboard as a USB Flash disk with volume name V2M-MPS2,but my PC can't recognize the MPS2+,I want to know what should I do.It seems that I don't install a usb driver,where can I find the usb driver?      I have applied for DS pro for a few days, I also write e-mail to ARM,however, my application is still pending.I want to know what should I do?