PHP的問題，找一下error.log再貼上來吧。
VM官方對於全白頁出現的說明：
Sometimes, due to a PHP error, a Joomla component such as VirtueMart can stop working and just show a blank page. This lack of display hides the relevant error message.
When this happens check the server error logs (not access logs) if you have access to them. The error message will show what the problem was.
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