How to turn on when on sleep mode

I just got my Ally X and after a couple of seconds of sitting down it seems like it goes on sleep mode. I try clicking the power button but it doesn't wake up. How do I wake the device up? I seem to be pressing everything with no response. The power light is on and appears white. I have to hold the power button for 10 seconds until the light goes away then press the power button again for it to turn on. Hope this make sense but any advice is helpful!