Just to make sure you are aware… initializing the disk is data destructive so if you are trying to access files that are already on the drive then your data may be missing or corrupt. If you are trying to set up the drive to be useable as a blank disk then proceed. Have you tried turning off antivirus or try different usb ports? If you have one available maybe also try a different computer to help determine if the problem is something on the drive itself or on your computer? You can try running the clean command in diskpart first to make sure all the old partition table info is erased but just be careful to make sure you are working with the correct drive.
-open command prompt and type diskpart
-run the command list disk
-find a drive that matches your drive size and type select disk 3 (or whichever drive is your portable drive)
-type detail disk This should give you details to confirm you are working with the correct drive. Mine says WD My Passport 0748 USB Device
-type clean This will erase all the data on the drive including the partition table.
-go back into disk management and try to initialize and create a partition.