You’re not alone, I have the same issue since two days (begun on Mar 25)
Have you find a solution or a workaround?
Circle and square buttons react but they have no effet.
Once an app is started, the only way to come back to the “desktop” is to use the return button (triangle) a lot of time.
Impossible to connect with usb cable to a computer as the notification to set the usb connection does not appear in the swipe down pannel.
When I swipe the upper panel, I can only have the “little” upper panel (first swipe down), the “large” upper panel does not show when I swipe down twice.
The little upper panel alway says than there no notification, even if the phone has just rung (received a SMS).
So when I hear the notification sound, i have to check the different possible apps (sms, whatsapp, …)
The backup dont work anymore: in the settings page, the last time of backup is in the afternoon before the problem begun.
And it seems that I can not install a new app from the market (the app stay in “waiting for download” forever)
I tried to reboot in safe mode, but it has no effect.
I’m afraid i will have to make a factory reset and lose some data