This has been an ongoing issue for a while not and quite frustrating...
Basically I've got Windows 7 Home Basic on my Mini 9. The install if fresh with almost no modifications done.
A few months ago, I used it, closed the lid, then returned to a piping hot netbook which was stuck on a black screen... I pull the battery and let it cool for a while then try again. Now when the lid is closed, the screen will go black (as the lid is closed) but never go to sleep)
To confirm it was some kind of software fluke, I booted to a live Ubuntu and confirmed it will sleep just fine when the lid is closed. With this confirmed, I reloaded Windows. Everything seemed to be fine for a while...until it started doing this again.
It's obviously the switch still works as I mentioned the screen does turn off as it closes... Power settings are all defaults, and I even checked and reset them to confirm all were right.
The only recent change I've done; I swapped out the wireless card and loaded the latest driver (Some Atheros BGN card; I forget the model right off). My previous Broadcom ABGN card was getting WAY too hot. I'm considering trying another card, perhaps an Intel 4965 or 5100... Not sure if the wireless has anythign to do with it though...
Which, BTW, it's not like the laptop can't sleep. You tell it to sleep, it'll go to sleep just fine and wake up just fine...