Information
Ensure that no device is connected to a virtual machine if it is not required. For example, floppy, serial and parallel ports are rarely used for virtual machines in a datacenter environment, and CD/DVD drives are usually connected only temporarily during software installation.
Solution
From the vSphere Client select the Virtual Machine right click and go to Edit Settings. Select the CD/DVD drive and uncheck 'Connected' and 'Connect at power on' and remove any attached ISOs.
or
From a PowerCLI command prompt while connected to the ESXi host or vCenter server run the following command:
Get-VM 'VM Name' | Get-CDDrive | Set-CDDrive -NoMedia