I attached my 500 GB external hard drive to my laptop, which had an assigned letter drive of E. I also attached a new 1 TB external hard drive to the laptop, for copying to it data from the drive E. Unfortunately, instantly, the new 1 TB drive took the letter drive E and the original drive E (500 GB) with all my data lost its letter drive. As a result, it is not recognized by the computer and all my data are virtually lost. Can somebody knowledgeable help me assign a letter drive to this disk drive, which is shown as "unallocated"? Thank you.