Answers to questions like these are typically noted in the Knowledge Base (just click on Help & Support) then "Contact Support" (bottom green button). For your convenience, this particular one would read:
"If your screen turns white when you try to login or are in the middle of game play it is likely that your graphics drivers are out of date. We recommend going to your graphics card manufacturer or computer maker's website to find out if there are any updated drivers for your computer. Once you get the updates try to run Wizard101 again. "
If that doesn't help you, please send me a ticket directly (same spot as mentioned above, just click the top tab "contact us"). Good Luck!
