Newly installed UbuntuMATE 18-04 does not boot
The first steps of troubleshooting could be
1. Run a LINUX from a live media, e.g. an Ubuntu Mate 18.04 live DVD,
by choosing the option to test Ubuntu Mate without installing it.
2. After the session started, open a terminal.
4. In the right upper corner of the gparted window is a selection box.
Select one drive after the other, perhaps you could see, that
something already is installed.
5. Mount all partitions, caja does provide mount options, but you not
necessarily get access to all directories, since the live DVD default
user might have UID 1001 and the /home/* of the installed user might
be owned by 1000, but there's no need to access /home/*. However, if
you want to acess it, run
and take a look by using command line only.
If you should see an installed Linux, e.g. run
the next step could be installing grub (not the packages, but the bootloader
to the drive).