The Disk 4 in My PC shows the message "Not Installed". But the disk can be accessed. What is the reason for this error?. Please Clarify.

If a disk is missing it is emulated from all the other disks by the parity calculation, the whole point, really. 

 

Go to Tools-diagnostics and attach the complete Diagnostics zip file to your next post. 

I expected you to follow up but since you haven't yet then I will add some additional information.

 

The state you are currently in, even though you can access the files in the "emulated" disk, is not correct or normal. (Actually, it is correct, just not good).

 

The emulation isn't actually reading the missing disk, if it is even attached. Instead, it is reading all of the other disks and calculating the data that would be on the missing disk.

 

And it is no longer protected by parity, since a disk is missing and single parity can only allow one missing disk.

 

You are going to have to get a disk assigned to that slot and rebuild it.

 

Is the missing disk the one that is actually displayed in the Unassigned Devices area?

 

Your next step to get things back to normal is to

On 5/14/2019 at 6:26 AM, trurl said:

Go to Tools-diagnostics and attach the complete Diagnostics zip file to your next post. 

Please don't try to do anything else without further advice.