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This should have been posted in Help & Support. There's a sticky thread there about common problems. I didn't see anything specific to your problem, but try this fix:
PVP.net Graphics Issues / Can’t See Store, Etc.
Nothing shows up when I go into the store / I get a black screen
1. Restart your client
2. Check to make sure you have cookies enabled in your Internet Settings.
3. You need to have TLS 1.0 & SSL 3.0 enabled, in Control Panel -> Internet Options -> Advanced tab, all the way at the bottom
4. Reset your Internet Explorer Settings
5. Make sure you're not set to "Work Offline" mode in IE.
6. Update your Internet Explorer.
The Lobby / Store does not display properly / at all
1. Reset Internet Explorer to Default Settings. Tools -> Internet Options ->
If that doesn't work, try a Repair on the Patcher screen (click the gears at the top right corner, near the Minimize and X). Also think about uninstalling your graphics card drivers and performing a fresh install of the latest drivers.