I'm stuck on the "Start Quiz" page.
If you are experiencing issues with Respondus Lockdown Browser not working properly on a Chromebook, it's possible you need to allow popups for Brightspace.
From Brightspace, click the Lock icon or Page Settings icon 
in the address bar:
Choose "Site Settings"
Find "Popups and Redirects" in the site settings, and change the setting to "Allow":
Your popup setting for commonwealthu.brightspace.com should now be "Allow", and you should be able to take a quiz in Lockdown Browser:
Popups are enabled, but I get blank, white screen.
If popups are enabled, and you getting a blank, white screen instead, you'll need to clear your cache and cookies.
- At the top right, click the Google Chrome Menu
and then Clear browsing data.
- Choose a time range, All time is preferred.
- Select Cache and Cookies. You do not need to clear history.
- Click Clear data.
You'll need to login to Brightspace again and attempt your quiz.