unrecognized USB drive after installing software on another computer

While installing software this morning on my wife’s new “surface pro 2”,  I used my portable USB where I save lots of data.  After installing some software a reboot was required.  I did not unplug the USB  drive.  Once the computer was restarted,  my USB drive read as “local drive D”,  a format is required to use the drive.   Panic set it.

I immediately we to disk management and changed the drive letter,   and rebooted the machine, and then I check to ensure that all of the newest updates had been performed.   They were ----  I started up the drive it still read:  local  drive “D”  reformat before using.    I need that data,    I hope there is a workaround.   I believe that during the reboot,  Win 8.1 must have written something to registry  (NOT sure why)   but I need to access that drive!!!!!!