Take a look at this tutorial titled: Learn Linux, 101: Runlevels, shutdown, and reboot. You can change from runlevel 3 (non-GUI Desktop) to GUI Desktop (typically runlevel 5) with the following command:
$ telinit 5
You can see what runlevel you're currently in with the runlevel command:
After running the above
telinit command you should see this change from a 3 to a 5. Some distros use differing runlevels, not sure about crunchbang, so you might need to double check which runlevel exactly is appropriate for GUI Desktop mode.
You can change which runlevel is the default typically through this file:
$ sudo nano /etc/inittab
# change this line (5 = Desktop)
# to this (3 = console)
Additionally during bootup you can override your runlevel via Grub by appending a number at the end of the
boot line. Putting a 1 there will tell the kernel to boot to runlevel 1 (single user mode). Putting a 3 there will boot to runlevel 3.
This is an example of the kernel line from the Grub menu:
title Fedora (188.8.131.52-106.fc14.x86_64)
kernel /vmlinuz-184.108.40.206-106.fc14.x86_64 ro root=/dev/mapper/vg_grinchy-lv_root rd_LVM_LV=vg_grinchy/lv_root rd_LVM_LV=vg_grinchy/lv_swap rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYTABLE=us rhgb quiet
Adding a number (1,2,3, or 5) at the end of the kernel line will force Grub to boot the kernel in that runlevel.