Clean install - Service Unavailable message at setup Folks:

I installed CraftCMS. All files are uploaded, chmod done, and everything else. I visit the page http://example.com/admin to go through setup and I get the message "Service Unavailable. Our site is temporarily unavailable. Please try again later."


I checked .htaccess and the config file. All is well.
I changed isSystemOn from "null" to "true". Same message.
I contacted my host to see if Craft will run on the server. All
requirements are met.


Since this is a Craft message it seems pretty clear that the database is being connected to but nothing is happening. Any assistance would be great.
Had similar issues. Found the problem was in the .htaccess file. 
Without code fixes, visit http://example.com/index.php/admin
instead of http://example.com/admin

Then fix your htaccess file later.