Install : Lost? And don't know what to do

I was installing Manjaro on my PC when my granddaughter decided to come in and say hello and accidentally hit the power bar and turned the PC off while it was just starting to install.

Now when I try to boot up the PC it says no boot, and when I boot from the removable I can get into demo mode, but when I try to install just errors saying can’t install.

boot from your installation medium
once in the GUI, make sure to unmount any partitions on your disk that might already exist and thus will get mounted automatically
use the file manager for that
then use whatever partitioning program there is (gparted or the KDE “variant” of it)
and remove all partitions and create a new partition table
(be very careful if you have another OS on there which you want to keep
you need to be selective in that case and skip the creation of a new partition table)

often it is sufficient to just create a new partition table if you want a fresh start

only then start the installer - it has now got “a clean slate” to work with

It likely does not work because some partitions are already mounted and just unmounting them will enable you to run the installer.