We're u able t c it before? I presume u must hav bin able to in order t copy from it? If it has stopped appearing in My Computer then it has likely died completely, but if it is in an external drive caddy or similar do check t wirin of t caddy... Also try pluggin it into different ports on t PC, n even a different pc if u hav one t hand, tho this probably won't make a difference.
Other things t consider - I trust u hav a fully up to date antivirus prog running, n hav run a full system check? Equally u might try an anti malware such as Malwarebytes...
U mention earlier u formatted this HD... Presumably u understand once u format that completely wipes t HD ie all data on it is lost?
After t format t drive should still turn up in My Computer etc tho... So still suspect t drive has died. How old is it? They don't last forever...