You have a hyper-v host and the disk space is reaching its limit although you have 4TB of storage.
Get-VM does not really tell you about the disk space each VM occupies. The space is mainly taken by the VHDs. I have put together a script to output an inventory report on the VMs on CPU cores, memory settings and total VHD size. This will give you an idea of which VMs take the most space on your host.
The PowerShell script can be downloaded from TechNet Gallery: Get Disk Space Used by VMs
Below is an exmple of the report in the PowerShell window:
Below is the same report output to the HTML: