I performed hard reset on my Nokia Lumia 710 (Windows Phone 7.5) and since then I can't launch Marketplace apps: I can download them, update them but when I start any marketplace app, I get black screen for 2 secs and screen returns back to main window or app window (depending where I start app). Additional resets did not help, I changed Windows ID but the change also did not help. Any idea what can it be?