vagrant does small things like
create an empty vm
copy disk from template
clear networking
setup port forward
boot vm
map shared folders
but once all is up and running, vagrant is not doing anything.
vagrant commands are sync, they stop when the command finish and you get the prompt back
I am sorry that you are in the cycle of crashes
what I will suggest is
do vagrant halt (this will stop the VM)
then using virtualbox gui, turn the VM on
if here still crash, is out side vagrant scope
if here still crash
i will suggest create a small VM that does nothing
mkdir p64
cd p64
vagrant init -m hashicorp/precise64
vagrant up
monitor
does this crash ??
Alvaro