Computer pops out of hibernate immediately

When selecting hibernate on my computer, it goes through all the motions, writing to disk, shutting down wireless, etc. - except, when the screen goes blank, it doesn't shut down. At this point, one of two things will happen:

1) If I activated hibernate through the console, the screen will pop back up exactly as I had left it, and the console prompt will return.

2) If I activated it through a menu or the power button, the screen will remain black and nothing will happen - and touching the mouse or any key brings up the login screen.

My pm-suspend.log file confirms that the computer is successfully going all the way into hibernate but then coming back out again instantaneously.

What's going on?

What sort of PC?

Can you please give us a few details on your PC and also what version of Ubuntu you are using? Also, have you been using the standby mode?
My own experience this happened on an older PC with an old version of Ubuntu.

I know this sounds strange, but the good news is it is easier to fix a fault when it happens every time.

4th Feb: I haven't seen any follow up, which could mean anything. I would suggest you try Googling for answers because that is what I did. Put in "Ubuntu" followed by your PC type and model and then a description of your fault. Because of the large number of Ubuntu users, it is probable that somewhere someone else has logged a similar to yours.