If you have previously deleted a virtual machine, it isn't removed immediately, but hidden for 45 days and the billing suspended. If you find you've made a mistake and want it back, you can recover it with:
$ bigv vm undelete old1
VM old1 was recovered
The machine will be returned to its previous state, have all the same IP addresses and discs reattached. You will be billed for it from the date it was deleted, but you will only be charged as if it had 1GiB of RAM, and any extra storage.
If you want to see the list of machines available to recover, you should use account show --include-deleted
