How sure you are that is in sleep mode? W8 uses a different shutdown/on routine. It´s called Fast Boot. It´s similar to hibernate but it only saves the kernel and controllers in the Hdd. Anyway press Win+x and go to Energy Options, there click on Choose behavior of the turn on/off button (the translation maybe is not the correct, ´cause my OS is in Spanish) and Change the configuration not currently available. Check if fast boot option is marked. In my opinion, you should not turn that off. It increases the boot time for sure.