When I try to turn it on it stucks in a loading screen, left it for a night - still loading. No problems with charging though.
I tried to reset it with Xperia Companion, but Windows recognises it as Unknown USB Device (Device Descriptor Request Failed). If I press a Volume-Down button before connecting it still identifies it as the same Unknown Device.
If I press a Volume-Up, it gets recognised as S1Boot Fastboot, but I'm not sure what to do with this. Tried to download Xperia drivers and apply them to this device, but no luck, it still isn't recognised by Xperia Companion, so I can't run its Software Repair procedure.
I've tried all of the above with a fully charged device.
The problem started when the tablet gets discharged, plus it was rebooting at the same time. So my guess is a software problem (something was rewritten in system files, and it can't start normally).
Is there any way to hard reset it with some tablet key combination?