The white page on the site is displayed due to an internal error on the site, which can be triggered by one of the three cases described below.
Try to enable outputting or logging PHP errors... Often after that, you can see the text of the error, which can be in determining the reason for the inoperability of the site.
Check information about disk space.
When you open a site, there is a call to certain site scripts. After being called, they can be physically overwritten on the server, but due to lack of disk space, they are simply reset to zero. In this situation, only increase disk space or deleting unnecessary files (cleaning directories with temporary files, cache, etc.). After that, you will need to reload the nullified scripts restore site from a backup copy for the date when no problems were observed in its operation.
There are also situations when a white page is displayed after the user incorrectly specified the database connection settings in the site's configuration file. The indicated data to connect to the database (instructions for various CMS can be found here). Sometimes the reason is an incorrect database prefix (tables with one prefix in the database, and another is specified in the configuration file - there should be no differences).