This will happens after the VPC get corrupted or when you don’t have password to logging to that VPC (Virtual PC).
1. First go in to Computer management window
2. Then right select the Attached VHD from the disk Management.
3. Brows and find the path of the VHD file and click ok
4. Now you can see that VHD file is mapped in your Volume table. Rite click on the Volume that you want to access and click Explore.
5. Once you want to remove this VHD from your PC volume list, right click and say Detached VHD