In a LiveUsb session (with persistence) i updated using
sudo apt-get upgrade
but it seemed to get stuck doing the "linux headers". The whole system froze-up. Prolly because i had too many things open a the same time. I couldn't even get a command-line to open to allow me to run
sudo reboot
or anything.

So, i had to force the notepad to shut-down by holding the on/off button.

Now the LiveUsb-stick wont boot-up and gets stuck on a command-line saying

BusyBox v1.20.2 (Ubuntu 1:1.20.0-8ubuntu1) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(intiramfs) Unable to find a medium containing a live file system

Is there any easy way to get the Usb-stick working again or will i get need to start from scratch again?
Regards from