Unable to delete file, files change?

Well, I'm trying to tidy up my hard drive and I noticed that some of my files have changed completely. I had a file containing a season of How I Met Your Mother copied onto my portable hard drive, and now noticed that season 1 has changed. The file name is all okay, but when you go into it, instead of having all the video files there, its changed to a whole heap of random files with names such as 7àáq*?}.▓┴% and ?·`í -u¤.┬│ü. I am unable to delete it as it says the file name is too long, and am unable to rename it so I can delete it. Going into properties of the folder, it says it's 505GB in size, but my portable hard drive is only 300GB capacity.



Is it a virus? What should I do? If anyone could just tell me how to delete it, I can recopy it onto my portable hard drive from the computer. Also, all the other seasons copied out fine, it's just this one. I'm thinking it's a virus that changes the whole folder and creates a whole heap of crap that you can't delete. Also, it occurred in other files on my portable hard drive too. Now I cant access those files as I have no idea what it is. One more thing, this is only occurring on my portable hard drive, my computer is fine.Unable to delete file, files change?
Two things to do.

First:

1- Download and install malwarebytes.

2- Run malwarebytes to scan your portable drive. If there's a virus it will find it and remove it.



Second:

1- Boot up in the safe mode and try to delete it from there, (Assuming malwarebytes did not detect a problem and no repaired action was taken.)