Second time that I run into the same issue with Vagrant. If you get a connection timeout warning like the following after vagrant up, this can have various reasons.
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
default: Adapter 1: nat
==> default: Forwarding ports...
default: 22 => 2222 (adapter 1)
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
default: SSH address: 127.0.0.1:2222
default: SSH username: vagrant
default: SSH auth method: private key
default: Warning: Connection timeout. Retrying...
default: Warning: Connection timeout. Retrying...
default: Warning: Connection timeout. Retrying...
If you have a box with a 64 bit system. One reason can be, that your BIOS prevents you from the virtualization of a 64 bit system. Normally you can change this in the settings of your BIOS.