I have been running MAMP Pro 3.05 successfully in Yosemite up to DP4 on a partition that was a clean install of Yosemite.
I now have run the installer for DP5 over m
Sometimes, it's not always the envars files that's the culprit. If you've been editing the vhost file at /Applications/MAMP/conf/apache/extra/httpd-vhosts.conf, a syntax error could cause MAMP's apache to not start without a warning.
In that case, you can run the following command and see if any errors are encountered.
sudo apachectl stop