HELP! Can't drag files from a folder into unity!?

I used to be able to..

but today i went to do more of my unity course and i was to add some audio files to my asset folder.

in the video they dragged and dropped it right in.

and just like i have done many times before, i went to do the same, but this time it would not let me. it had the circle with the slash through it on my cursor.

this is so annoying, and slows down my workflow. i know that i can just drag it into the folder location on my hard drive and that works. but i need to solve this stupid issue.