laptop sometimes shuts down when i click sleep.

I have a brand new Toshiba Satellite laptop 64 bit OS with Windows 8.1 . When im done with the laptop, i always click "sleep" but when i return hours later, its only a 50/50 chance that it is actually sleeping with the power button flashing. The other times it appears shut down - but not in a true shut-down mode...the power light is not flashing, yet if i push the power button it lights up continuously yet the screen stays black forever until i finally have to hold down the button and do a hard restart. I bought another exact same laptop for my work about a week before and i dont have the same problems with that at all and the settings seem to be exactly the same.
What could be the problem?
Thanks in advance for any possible help.