Why is my computer asking me to format a disk ?

So I plugged in my external hard drive to my computer, but when I tried to open it to see my pictures and music, the computer wouldn’t let me.

It told me that I would have to format the disk before i could use it, and I don’t want to do that because I don’t want to lose my files or pictures.

Does anyone know how I can see and copy my files, without formatting it ? I’m scared if I do it will erase everything and I don’t want that to happen.

It used to work a few months ago, I didn’t have a problem with opening the hard drive. The only thing I can come up with is I have too many files on it. But I’m not sure what gives.