Have exactly the same problem Just a blank screen, and in the sidebar no preview.. Can't logon because it displays nothing.. Thing is, it's only on my work-Win8 notebook.. My home win8 notebook has no issues with this.. Though that's a Intel GMA950 device, where at work I'm with a Radeon HD2600..
So the weird thing: It worked in the past. Somehow this bevaviour has popped up. Still get messages, but can't actually open the app. When I uninstall the app, and reinstall, the settings are retained! Still getting messages and everything, but same behaviour..
When I uninstall the app, it's also removed from %ProgramFiles%\WindowsApps so no cached info there.. There are remnants in the registry, but they address merely notification history, icons etc.. Just to be safe I removed them too.. %appdata%\local\Packages also did nolonger contain information about PC Monitor.. Cleared all temp folders, restarted, ran CCleaner. Also found two extra entries of "MMSOFTDesign" in my %appdata%\local\Microsoft\Windows\Live\Roaming\LocalCache folder. I figured these are the settings from Metro apps which are synced to the cloud to sync the app settings across different Win8 machines. Deleted them too for good measure.
Still no luck. Darn.
Colleague of mine said that roaming cache of your live account is only deleted after 30 days of 'inactivity', which means that if the app is deleted from all your Win8 devices, only after 30 days the roaming cached data is deleted..
Perhaps I'm missing something, but can anyone shed any light on this? Of perhaps Matt can suddenly remember what the solution was and help us all