Test this:
Switch on your computer.
Press and hold the Shift key, which will bring up the Grub menu.
Select the line which starts with Advanced options.
Select the line ending with recovery mode
Your PC should display a menu with a number of options.
Select In this order: Network -- Drop to root shell prompt.
In the terminal run:
mount -o remount, rw /
mount --all
apt-get update
apt-get install --reinstall aptitude deborphan ppa-purge
aptitude remove '?and(?reverse-depends(elementary),?not(?reverse-depends(?exact-name(ubuntu-desktop))))'
apt-get install --reinstall ubuntu-desktop
apt-get dist-upgrade
deborphan
apt-get --purge remove $(deborphan)
deborphan --libdevel
apt-get --purge remove $(deborphan --libdevel)
deborphan --find-config
dpkg --purge $(deborphan --find-config)
apt-get autoremove
apt-get clean
ppa-purge ppa:elementary-os/daily
reboot