Inspiron Waking by Itself, While Shut!

I've got an inspiron 1720 and i have noticed something strange that has happened about half a dozen times. when i shut the lid, it's set to sleep, which it does. the weird thing is that sometimes when i wake up in the morning, the lid is still shut but the processor light is blinking/ on and my wireless usb mouse is lit up(on). for some reason, the fan does not run when this happens and it gets pretty warm. if i open the screen and type in my password, nothing is happening. close the lid and it goes back to sleep like normal. i changed the time for my automatic scans and updates so that they are all during the day and it still happens. anybody ever heard of anything like this or know how to fix it? it's like my computer is waking up by itself... i did reboot to factory display(i think thats what it's called) about a month ago and i never noticed the problem before that but i was experiencing some other problems. also, when i have my microsoft wireless usb mouse plugged in, the screen saver never comes on even if i dont touch the mouse. is this because the computer sees usb activity thus thinking the computer is in use? can i change it?
i'm running vista home premium.
Thanks!