Try this:
Start in text-only mode
Switch on your computer. Wait until the BIOS has finished loading, and press and hold Shift, which will bring up the Grub menu.
Select the line which starts with Advanced options.
Select the line ending with (recovery mode)
Press Return and your machine will begin the boot process.
After a few moments, your PC should display a menu with a number of options, including Drop to root shell prompt. Press Return with this option highlighted.
The PC will start in a terminal.
Run these commands:
Mount partitions in read-write mode
mount -o remount,rw /
mount --all
Update repositories
apt-get update
Install aptitude and deborphan
apt-get install --reinstall aptitude deborphan
Eliminate the components of lxde that are not necessary in xubuntu
aptitude remove '?and(?reverse-depends(lxde),?not(?reverse-depends(?exact-name(xubuntu-desktop))))'
aptitude remove '?and(?reverse-depends(lubuntu),?not(?reverse-depends(?exact-name(xubuntu-desktop))))'
Reinstall xubuntu-desktop
apt-get install --reinstall xubuntu-desktop
Eliminate orphan packages
deborphan
apt-get --purge remove $(deborphan)
deborphan --libdevel
apt-get --purge remove $(deborphan --libdevel)
deborphan --find-config
dpkg --purge $(deborphan --find-config)
Remove unnecessary packages
apt-get autoremove
Remove downloaded packages
apt-get clean
Restart system
reboot
apt search --installed "*lxde*"
andapt search --installed "*lubuntu*"
– ridgy Jan 13 '17 at 17:59