Buffalo provides Data Recovery services. Read about it here.
Unplug the drive and reboot your computer. Once booted, insert the DC USB cable into the drive and your comp and wait a few seconds, THEN plug in the attached USB cable into your comp. If at this point you can access the drive normally then the unit is not getting enough power through one USB port therefore you need the additional DC cord.
What Windows version are you running?
What Filesystem is on the drive?