Do you have a directory named ".ssh" in each home directory with some files in it? If not, run this as a regular user:
You should copy the ~/.ssh/*.pub files on each PC to the other PC into file ~/.ssh/authorized_keys. The .pub files are not secret, so you can copy them by ftp or a public directory or whatever. Each .pub file is one very long line, and the authorized_keys file has nothing else but these very long lines.
If you change something after you've logged in once, the entry in ~/.ssh/known_hosts on the othe PC may prevent you from logging again. So if in doubt, delete the known_hosts files and allow them to be regenerated.
To login by password, you must not have "PasswordAuthentication no" in either /etc/ssh/sshd_config or /etc/ssh/ssh_config.