On those machines, Zorin OS 15.3 Education Lite should work fine and is supported until April of 2023.
As FrenchPress pointed out, a common cause is filled RAM. At 4 gigs on 15.3 Lite, you would need a lot of Browser tabs all open and running at once to do that...
Another is Battery on notebook computers. If the battery is failing, it can cause the battery monitor to be unable to make the correct detection. Some resolve this by disconnecting the battery and running the notebook as simply plugged in - or replacing the battery. Replacing or removing the battery should be done only if the battery tests as bad.
With Administrator Privileges, you can check the /var/logs/ for log files (You can use pastebin to post them here for help reviewing them. They can get quite lengthy).
To Access through GUI:
Open terminal with ctrl+alt+t
Enter in:
pkexec thunar
Click the UP arrow icon on the top toolbar to the topmost level that is Root (/). Here, you will see /bin, /dev, /etc... and /var
Click open /var then /log and scroll down to the text file:
xorg.log
dpkg.log
kern.log
syslog
Start with Syslog and xorg.log.
. Instant download for me 

