Problem with sleeping

Sometimes, when I close the lid on my macbook, and reopen a few hours later, the following happens:

While the macbook (unibody) is closed, the breathing light (the little white on the front) is lit solid (i.e. not coming on and off as during normal sleep). When I open the lid, the light goes out, and the macbook is completely unresponsive. The only way to get it up and running again is to hold the power button down until it shuts down, then restart.

Why does this happen?

 

Hmmm I did install 2x2GB of RAM, but this was about 2 months ago and I only started noticing the problem recently. As a matter of fact, I only started noticing it when I installed that monitoring widget (the one that monitors temp, fan, ram, hdd, etc - the name escapes me now), which I have since uninstalled. Funnily enough I had similar problems with my white macbook also after I installed that widget.

Update: I think it has something to do with my BT mightymouse. It seems that when the mouse is clicked while the machine is sleeping (can happen very easily since I routinely forget to switch off the MM and just chuck it in the bag), the MB sort of wakes up and goes into this mode. Hmmm, I will investigate this a bit more.

 

Yep, this was the culprit. Thanks. I thought it was unchecked but when I looked it wasn't.