Some ideas:
Do you have a camera to take a photo of your current desktop environment?
It is possible to delete the persistent image file and create a new one. It is unnecessary to do a full reinstall from the CD.
Are you able to switch to a console with the key combination Ctrl-Alt-F1? There you could issue the following command which will open a terminal window on your desktop environment.
Code:
chvt 5 && su -c "DISPLAY=:0 lxterminal -l" knoppix &
In the lxterminal you could try some commands.
Code:
killall lxpanel
lxpanel --profile LXDE &
If you have lxpanel running but still no nm-applet then you could try
Code:
killall nm-applet
nm-applet &
In the lxterminal it is possible to start synaptic package management