Default [Q] Tablet doesn't turn on


I have successfully rooted my GT P7500 and installed ClockWork Recovery. When I tried to create a backup in it, the backup process got stuck. Probably because lack of free space during the backup process as there was a lot of data. So I tried to reboot the device - first time it booted up and got stuck on homescreen. So I had to reset it. After reset the device does not start at all - display is off (no reaction), battery is fine (was around 50%), even putting on charger does not do anything to show up on display.

Is there a way to do something about it? A special "reset" or anything?

Thank you for any advice.
Device: Samsung Galaxy Core (I8262)