i am just assuming you get graphical error, as i froze last time that i used nvidia graphic.

did you configure your graphic to be such nvidia, or others? in driver manager before this error?

but first thing, to go go the terminal while in the black screen try to use ctrl+alt+ f1-f6, just try all of them until you get into one of them, cause you onyly posted using ctrl+alt+f2 which it didnt work. So try again and see what happens.

secondly, try to remove your graphical diplay by using , for example sudo apt-get purge nvidia*. -> nvidia* means purging all of the nvidia components. then reinstall then using, for example sudo apt-get install nvidia-current-updates.

finally restart your PC.

point to be noted, sometimes when you are in the terminal, you are not automatically connected to the internet, using nmcli d wifi connect [name of your SSID] password [your password] wlan0 .

To enable persistence you have to:
1.) Create a new partition with ext3/ext4 and call it "persistence" (e.g. with gparted)
2.) create a new mountpoint: mkdir -p /mnt/kaliusb
3.) mount the partition from 1.) to this mountpoint: mount /dev/sdc2 /mnt/kaliusb
4.) create the persistence.conf file in it: echo "/ union" > /mnt/kaliusb/persistence.conf
5.) unmount the partition: umount /dev/sdc2 6.) reboot and select the "with persistence" option at the kali boot screen

After that all your changes are saved. Refer to: https://docs.kali.org/downloading/kali-linux-live-usb-persistence for details and how to make an encrypted persitent partition* (it's really easy and nice explained (kudos to these guys)

*you can do all this while runnng in the kali-live environment on the same usb stick (refer to: https://docs.kali.org/downloading/kali-linux-live-usb-install) - that assures, that you have all tools like "cryptsetup" in place