Eh.
Windows has NEVER gotten the hibernation thing down right yet....
FYI: You didn't say anything about what OS you're running, so I'm going to have to assume XP.... (Also cuz if it's Vista I haven't a CLUE, so you're on your own there anyway!)
Okay, Good News / Bad News time!:
Bad News: It is SOOO complicated to work out what and why this happens - it's like 15 different entire
scenarios to follow/check in the MS knowledgebase article about it - it's simply not worth the time to figure out in detail. However!:
Good News: It's ALMOST ALWAYS one of three things:
1) A scheduled task, 2) A running service, or the MOST LIKELY, 3) network activity.
Oddly, I'll have you check them in reverse order (since that puts the easiest checks first)....
3) Start -> RIGHT-CLICK "My Computer" and select "Properties" from the popup. Then the "Hardware" tab, then the "Device Manager" button.
Click on the plus sign ("+") in front of "Network adapters" and
FOR EACH DEVICE LISTED do the following:
Right-click the device and select "Properties" from the pop-up. Select the "Power Management" tab. Assure that the box for "Allow this device to bring the computer out of standby" is NOT checked.
Select "OK" button to close device properties, and "X" out of other popups.
2) This one's a toughie.... We're going to try to see what the Event Log says happened when your system started up. You'll need to do this AS SOON AS POSSIBLE right after it wakes itself to increase your chances of finding it....
Once it wakes, log in to an account with Adminitrative privleges and do the following. (If you can't find this first menu item you'll have to skip this part....):
Start -> Control Panel (->) Administrative Tools -> Event Viewer
Scroll down to find the first event with a "Time" around the time when the system just woke up, and dounle-click that event to bring up the "Event Properties" popup. (The first event should simply display info about the version of Windows that is running.)
Select the Up Arrow button, and jot down the name of every SERVICE that it reports as having "entered the running state" until you reach the top of the event list and get the popup "You have reach the beginning of the event log. Do you want to continue form the end?" and elect the "No" button and "X" out of all popups.
PM me your list of services.
1) See if a scheduled task is waking your machine. (AntiVirus SW does this a lot. YA reason I don't use the big commecrial ones!)
Start -> Control Panel -> Scheduled Tasks
If only "Add Scheduled Task" is there you're done.
Otherwise, check each task to see when it's scheduled to run.
The one set to "every hour..." MIGHT be a clue!
"X" out of Tasks window(s)....