Here are the known causes of blank or 'white' pages:

The most common cause is a PHP failure. The Mambo 4.6.x versions all require PHP4.3.0 and higher (PHP4.4.x and higher is recommended).
Please see the system requirements here: http://forum.mambo-foundation.org/showthread.php?t=1914
If you are running the correct versions of PHP and get unexplained blank pages you should contact your host. The server logs should provide more information about the cause of the failure. If you are hosting your own site , try increasing the paging limit in your php.ini file.

Other possible (but less likely) causes may include:

• The Mambo files were not uploaded correctly or have become corrupted. Upload the Mambo files again and make sure you overwrite the ones on the server. Reupload the Mambo image files in Binary format. All other Mambo files, such as php, js, html etc must be uploaded in ASCII format. Most FTP programs automatically determine the correct transfer mode but it pays to check your FTP client settings to make sure of this.

• There are extra spaces or lines in your template's index.php file. Make sure there is no whitespace or extra lines in index.php either before the <?php or after the ?>. This also applies to comments. The top line of your template's index.php file must start with <?php

• You have a bad extension installed. If you have recently installed a new extension try removing it.

• The servername setting in configuration.php is wrong. Doublecheck this setting. 99% of the time, 'localhost' is correct:
  $mosConfig_host = 'localhost';

• The absolute_path in configuration.php is incorrect. $mosConfig_absolute_path = 'path/to/your/Mambo/';
  If you are unsure what this path should be, check with your host

• There is a blank index.html file or index.htm file in your site root and your server calls one of these file extensions before it calls index.php. Remove the blank or white index.html file.

Note: incomplete uploading or corrupted files, or incorrect paths, will usually result in an error message showing on your site. It is extremely unlikely that they would result in a blank page, but the bullet points are still things you need to check if you get blank page issues.

Turning Site Debug ON in your Mambo global site configuration may provide additional information for troubleshooting.