I have a HP Probook 6450b laptop, running Windows Professional 7 (64-bit) operating system. Just recently the laptop has exhibited symptoms that when it is placed in Sleep Mode, it enters Sleep Mode normally - but when the Power button is depressed to bring the laptop out of Sleep Mode, the laptop reverts to Start-Up, as if it had not (been) shutdown properly.
So, this is not a problem where the laptop enters Sleep Mode, but then won't wake-up - it just wakes up, but not as it should as if it were immediately coming out of the low-power Sleep Mode. The laptop will still (normally) go into Hibernate Mode, and Resume, when the Power button is pushed.
All my settings under the Power Options appear to be unchanged and set correctly - so that the laptop should enter Sleep Mode, and wake-up normally. I've tried and researched as much as I think I can - but I've got to believe that someone else has experienced this same problem, and maybe even has (stumbled on) a solution. I'll actively monitor this posting, if there are follow-up questions or even proposed solutions, that I might want to give a try. Thanks!