Your issue might be because some devices are automatically waking, or keeping awake, your computer.
You can try disabling these.
Open the Command Prompt again (choose Run as administrator).
Type the following command. This will reveal all the devices that can wake up Windows 7.
Powercfg -devicequery wake_armed
You can then disable a device by typing in the following command. Replace devicename with the name of the device listed.
Powercfg -devicedisablewake “devicename“
You can also disable a couple of items, which might be causing the problem, in the Device Manager.
Open the Control Panel, click on Hardware and Sound and then click on Device Manager. Or, if in icon view, just open the device manager
Expand the device you want to disable and right-click on it and choose Properties.
Click on the Power Management tab and uncheck the "Allow this device to wake the computer" box.
The Mouse can be a culprit, but of equal importance can be the Network adapter. Click on it and right click any items which are shown underneath, then follow the procedure above.
Why the mouse? Well, I have experienced with users, that (particularly wireless mice) can due to continued distrurbance, send enough activity to keep the computer awake – worth a try?