I've read what I've found about this problem..
In most of the cases this problem occurs after installation of a ROM or some adjustments being made. In my case, I was just browsing when it rebooted itself and got stuck on the X screen (just after the Google screen).
The options that I've found in the forum are:
1) Use Nexus Root Toolkit to reset, unlock, root and possibly relock the tablet.
2) Simply go Bootloading > Recovery mode > Wipe data/factory reset.
Unfortunately, both options involve erasing all the data from the device.
Is there any way to recover the device (turn it on) without loosing the data / how?
Thanks in advance!