It's just that. The kindle fire turns on, loads up as normal with the logos on screen, but then the screen is black. I've have another kindle fire (that works) so I checked where the brightness controls would be on screen and tried to turn them up. It doesn't appear to be that. If I press the power button the 'do you want to shut down your fire' warning up pops up as normal, perfectly bright, just against a still black screen. What's going on and how can I fix it?
CombatWombat's response is spot on. In addition to that one suggestions from me would be to take off any cases you might have, just in case they block the ambient light sensor (depending on which device you have exactly).
Thanks for your advice CombatWombat and Anne B. I removed the case and gave it a go holding there power button for a slow 30 seconds and then turning it on. After the fire logo I'm back to the black screen and no functionality. I notice my working tablet shows the fire logo briefly and then loads up normally, whereas the broken tablet shows the fire logo for a very long time before going to the black screen. i think maybe it's time to buy a new one