Do you have a USB keyboard and Mouse?
It could simlpy be down to your USB keyboard & Mouse.
Go into the device manager properties for your mouse and keyboard if they are USB
and go into the power management section and verify that "Allow this device to bring
the computer out of standby" is not checked.
Any USB device that is set up to bring
the computer out of standby needs a power source to operate, so the computer leaves
the power supply in the normal mode, keeping the fans on, and supplying power to
the usb root hub for the device. Maybe that helps some of you?