Could not able start the instance which in "error" state

Question

Could not able to start the instance, getting following error.

$ nova reboot <instance-name>
ERROR: Cannot 'reboot' instance e54b5d26-2918-4ab6-8210-94e827bf2a94 while it is in vm_state error (HTTP 409) (Request-ID: req-88efe1d4-37c3-409e-89a9-844f537e51eb)

$nova show <instance-name>
| fault                                | {"message": "Instance e54b5d26-2918-4ab6-8210-94e827bf2a94 cannot be rescued: Driver Error: internal error: early end of file from monitor: possible problem: |
|                                      | 2016-05-01T05:35:27.071764Z qemu-system-x86_64: cannot set up guest memory 'pc.ram': Cannot allocate memory 

Please tell me how to resolve this issue.

Solution

nova reboot --hard Instance_Name

worked for me.

After I typed this command, I received

Request to reboot Server ( Server:Instance_Name) has been accepted. 

My instance started running back then.