[Q] How did this happen?! Help pls! topic

So, my phone has been on airplane mode for a couple of weeks now as I'm abroad in India. I've only been using it for taking a few pictures and taking notes in the calendar app

I took my phone out to take a pic, and just after I pressed the camera button, the screen froze. I waited a minute or two, still frozen. I pressed the power button, and I think the screen went off (can't quite remember now). Anyway, to get out of this I held the power button down, and the 'back' and 'home' buttons started flashing, and then I was in fastboot!

Here's the thing; It says

*** TAMPERED ***
*** LOCKED ***

at the top. I've searched and found a few threads, but all of them that have the same problem are when they are trying to install a ROM, or S-OFF or something like that. However, I have not done anything at all to this phone, no unlock, no S-OFF, ROMs etc....

When I try to get into recovery, the HTC Powered by Android screen comes up and the graphics are garbled at the bottom, and it goes back to fastboot after a second or so, and this time it says:

*** TAMPERED ***
*** LOCKED ***
*** Security Warning ***

at the top of the screen.

Tried Factory Reset- same thing

So, my question is how could this even happen?? And also, how do i get out of it?

I can't get my getvar all yet because I've only got a Chromebook with me, so no ADB yet, will try to set up Quinny899's guide to get this sorted. I might be able to get to a Windows laptop later tho

Any help would be appreciated, can I recover from this without losing data??

Thanks in advance

what would happen if I try to flash a custom recovery on a locked device? topic

I have bought a used TF300T. I want to install on it a custom ROM.
I can't unlock using the Asus tool (version 8 on system 10.6.1.15.3), probably because the serial of the tablet is already registered to the previous owner.
If I go on with the guide for making unbrickable the tf300t on AndroidRoot dot Mobi
what would happen?