External hard drive is shown on Disk management but is not shown on my computer, also not able to change the drive letter.

[sanjokgrg23]

My external hard drive is shown on disk management but is not shown my computer, and when I do a volume list on cmd, the main hard disk is not shown. So I dont know what is happening how can I fix this.

 

[jbseven]

what is the error message in computer management when trying to change the letter?