Trying to fix the installation you currently have will be fun.
If you are connected to the internet you can type this command in a terminal
sudo apt-get install -f
hit enter, type your password, and let it run. once it is done type
sudo apt-get update
let that one run too, once is done type
sudo apt-get upgrade
let that one run too. a reboot might be necessary after that last one but might be not, so type
sudo apt-get install lubuntu-desktop
and let it run just like you did previously.
Let us know how that goes