Incase you own an ASUS Transformer (probably should be applicable on other android tabs as well) , and wondering why your tab doesn't power on when you left it unused for a while, then this is how you can fix it.
You need to follow the hard reset procedure to get it back alive.
Steps to reset :
- Press the power button (Top Left)
- Press the volume rocker (down) which is on the Left side of the tab when you are looking at the screen.
I am not sure of why this happens though, but my understanding is that it happens generally when there is some corrupt data loaded in the cache of the tablet.
Hope this helps.