1
Is that 1TB external drive a USB 3.0 drive, and if so, are you connecting to a USB 3.0 port on your Dell laptop and have you tried connecting the external drive to another USB 3.0 port..
2
You mention you started copying the files by genre, where are you copying the files from is that from inside File Explorer or from inside a media player app.
3
Right click the folder you store your MP3 files in File Explorer and select Properties.
Please provide a screenshot of the resulting properties dialog box.