Issues with itunes

Hi, when using iTunes I usually change the preferences so everything saves into my external hardrive, all my music is on it. I never had an issue till now, iTunes has just updated and it wont pick up any of my music that's saved on the external hardrive. I looked under preferences and its changed back to being on my computer to save all media files, when I change it back, it never stays, any idea if I can solve this or will I for now on have to transfer all my music back on to my computer? I also have windows 10 which I don't know if this could be effect of this.

Kind regards

Worzel