N810 works perfectly after power-on. Also fine after short hibernation. If started up after period of hibernation (say 10-15 mins +), then none of the hardware keys work, and touchscreen is slow to respond. After 30-60 seconds, the device resets itself.

My OS is up to date, and I have tried resetting all the settings.

I need some advice please - is there anything I can do to fix this?