Do you have MySQL server running before installing iRedMail? Do you set a password for MySQL root user?
Here's my suggestion: iRedMail is designed to be deployed on a FRESH server, so you'd better install a minimal server to install iRedMail.
Also, next time you install iRedMail, try using below command instead of "bash iRedMail.sh", it will print addition details on terminal, please paste it here to help troubleshoot if it failed again.
# IREDMAIL_DEBUG='YES' bash iRedMail.sh