It' happened with me one time and the cause for me (I cant be 100% sure) it was because of heat, at that time I didnt check for temperatures in the disk and it reached 60degrees for around 3 months, one day the disk was gone from the pc, exactly the same as you, basically windows detects it as a disk without any format but don't format it if you have valuable data you can still recover some of it.
There was no way to restore it as it was before but I managed - with recuva and another similar soft that i dont remember the name now but most of them are basically the same - to recover many files that were still in the disk.
My suggestion would be to recover what you can, format the disk and do many test to check if it is working fine, because rma wont do anything if the disk is working fine since it might not be actually broken or anything... for example western digital needs some specific errors in smart for you to be able to RMA it (spin up time, reallocated sectors and raw errors).
From what I understand is that the disk is like a book and it has an "index", sometimes that index breaks and so the files or "chapters" are not accessible anymore, they might be still there but without that index the disk doesn't know where is anything so is like it's gone. (sorry for the poor explanation)