My apologies if this device already has its own thread. I searched before asking, came up blank. I also googled the issue before coming here, couldn't find anything that fitted.

My 83 yo Dad has one of these tablets. I got it for him when I got mine, neartly 2 years ago. He's now finding that the screen goes black after just a few seconds, and I can't find a setting to change this. Tablet sleep time is set to 30 minutes of inactivity, and I have been scouring the settings looking for anything that might explain this behaviour. It effectively renders his tablet unusuable for him, because he has to use a stylus, and is just learning how to use the tablet. So he "types" with (let's call it) deliberacy, but now by the time he's ready to press the screen, it's black. 

The tablet is functioning fine, when the screen is active, if a user types fast enough, it's OK. Any suggestions on how to fix this problem?  

EDIT: I've contacted the person who now has the other one we bought on the same day, she says hers is working fine.