I have had an external 1TB 'WD Elements SE' disk for almost a year now, and it has worked perfectly until a while ago. It's split into 2 partitions, 1 is 100gb and the other is 900gb. Last week I noticed that the files and apps on the 900gb partition would not open. Then a few days later the 900gb partition stopped appearing on my desktop, so I erased it via disk utility, which was a success, but it still won't mount. Now I went to check on it today and the files on the 100gb partition cant be opened any more, and nothing except my Mac's internal hard drive appears in disk utility, despite my 100gb partition still showing on the desktop, so I can't do first aid or erase anything. I get exactly the same thing when the SDD is plugged into another Mac. Is the SSD dead or is there a way I can erase and reformat the entire disk to try to get it working?