There are following reasons for a slow VM:
- Check the CPU, RAM and HDD meets minimum requirement for the OS installed on the VM.
- Check CPU, RAM and HDD usage on the VM. CPU and RAM can be checked using Task manager -> Performance. To check which resource uses lot of resource, click Processes tab in the Task manager. You can sort in ascending or descending order based on the resource usage.
- Check the Network speed. Try to ping the VM and note if there are any latency or ping drops.
- If you are trying to access a VM in Vcenter console, make sure the VMware tools is installed on the VM. Without VMtools, working on Vsphere consoel will be very slow.
- Low CPU, RAM and HDD allocated for a VM that has a modern OS and needs more resource.
- If the HDD is having lot of activity, low CPU and RAM would only reduce the speed. Make sure to add adequate resource on these VMs.
- Checking whether any of the following are happening on the VM:
- Altiris patch scanning
- Symantec Endpoint Protection or other AV scan
- Windows update installation
8. Other rare cases includes, high resource usage caused by Virus / Worm.