go into the root of the drive (thats the directory at the top of the drive)
hold controll and press a
this will select all the folders and fileso n the drive
right click on one of the files/folders and select properties and untick "read only"
click on apply then when it asks you select apply to all sub folders
if this dosnt work you may have to copy all the files over to your pc then format the hdd then transfer files back onto it