When a snapshot removal (consolidation) is in progress, you cannot perform other VM tasks, such as power operations, or vMotion migration, in the virtual machine. You must remove the snapshot without any interruption to ensure data integrity. Based on the amount of snapshot delta to be committed, the amount of time varies.
This article outlines the actions taking place against the virtual machines snapshots.
Note: Verify if the Virtual Machine is in responsive state by performing a ping test or trying to access the VM through RDP.
Understanding virtual machine snapshots in VMware ESXi and ESX (1015180).
Best practices for virtual machine snapshots in the VMware environment (1025279).
Delete all Snapshots and Consolidate Snapshots feature FAQ (371714).
Estimate the time required to consolidate virtual machine snapshots (2053758).