Sometimes, customization process of the virtualbox images can take some time and affect lots of specific options that vagrant cannot deal with.
Anytime virtual machine can be started with
VBoxManage command any time.
For an instance lets get list of available vms:
~ VBoxManage list vms
Should display list of all available vms.
Lets start one of them:
~ VBoxManage startvm myvm --type headless
myvm is a name of the vm from the list.
--type headless meant to start virtual machine without any gui (very helpful on workstations or servers without an X server running).