Software up to date
Check that both your ExpressionEngine (EE) software is up to date as well as your third party add-ons.
Nothing is Perfect
You may have done everything correctly but bugs exist in all software and it could well be the issue here. Check Ellis Lab Bug Reports If you do happen to find a bug, help others and report it.
Platform up to date?
Check that your PHP version and modules are satisfactory.
It may be one of the smallest files but it’s incredibly easy to get it wrong. If you have url or form issues then check your htaccess file.
Open Base Restriction
If you are working with Multi Site Manager (MSM) then it’s likely that you will need to lift this restriction.
A white screen is as good as useless, you need to find that error. By changing debug =0; to debug = 1; in the sites index.php file you will glean the error(s).
When shifting environments it’s very easy to have the wrongly set template path.
More info from EE
$config[‘template_debugging’] = ‘y’;
$config[‘show_profiler’] = ‘y’;
Will give you some handy information about your build and processes.
Isolate the problem
If you have tried all of the above then it may be time to put some real effort into it. By wearing away the extras and starting with a basic set up can help get to the bottom of the matter. You may need to remove add-ons, templates and assets.
Good is your best friend in times like these. It’s highly likely that someone has come across the problem before. Even if someone has been hit with something close you may get an idea of successfully troubleshooting the ExpressionEngine issue.
Ask for help
You should be able to fix most problems your self from the above information. If not it’s time to ask for help. Give as much detail as possible and your build info.