I'd recommend the following:
1. From within the BIOS: "ACPI Suspend State" should be on "S3 State"
2. From within the Operating System:
2.1. Under Device Manager: Make sure both, the keyboard and mouse, have the "Allow this device to wake the computer" option turned off (unchecked)
2.2. Under Power Options (in Control Panel): Locate an option entitled "Choose what the power buttons do"; once that window is up, select "Sleep" where it says "When I press the power button:" Apply the changes before exiting.