Hibernation problem

Using SP3 with all updates on a desktop, if I resume after hibernation but
do not click my logo on the login screen within a minute or so the computer
shuts down again.

How can I stop it shuting down unless I tell it to?

It is really anoying to get a phone call just after restarting the computer
and then finding that when the call is over the computer is not up and
running unless I remember half way through the conversation to go and click
the startup logo. All my power option are set to never power down uhnless I
click a button to do so.