webpages is halted by the combination of NGINX and PHP-FRM

You should look at the last lines of that website's log files:

access log: /usr/local/apache/domlogs/yourdomain.com.log
error log: /usr/local/apache/domlogs/yourdomain.com.error.log

Should give you a pretty good clue as to what's going wrong.

main page was giving 500 error but when going to wp-admin it shows database error, rebooted, no good, reset mysql password for this user account and then it was working fine.. i checked logs, nothing that stands out.. but i also noticed there were some modsecurity hits, can modsecurity lockdown a website from future attacks? is that what happened in my case, or could it be some sql injection that changed the users database password ?

I'd recommend you hire a sysadmin to check your server or use CWP support. Nobody will guessing on the forum