You can safely remove all files in the home directory, because they are recreated, apart from files copied on user creation from /etc/skel, so

#!/bin/bash



shopt -s dotglob 

rm -rf /home/username/*

sudo -u username cp -a /etc/skel/* /home/username/

where username should be substituted with something meaningful.

Per your request ("when computer starts") this can be executed from /etc/rc.local. More likely, you want to execute it between each to logins, so put it under /etc/gdm/PostSession or /etc/gdm/PreSession.