Hmm its a weird one.. Ok, just to make sure that we are talking about the same thing, if you go to the 'edit plan settings page' (which as you know, is accessable via the power options page with 'change power options' in blue writing) you get two options.
1.Turn off display
2.Put the computer to sleep
As you know you can change the times to suit but the dialogue box I'm thinking about is accessed via the small blue writing which says 'Change Advanced Power Settings' its here you can make further changes under Sleep. If however you've already tried that do you have a USB device plugged in? If you have a mouse plugged in for example then go to Device manager and right-click on the mouse. You should see a option about waking the computer, I think you need to unclick that and any other device that may have a similiar effect. Also you might have to unplug these devices when you want the laptop to sleep as the machine will keep 'talking' to them. I hope this has been some help. Let me know how you get on...

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