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I scheduled a task in Windows 7 to play music at a particular time of the day. The scheduler allows a setting that makes the laptop power up from Sleep/Hibernation mode automagically. I guess that would be some setting that windows does on the BIOS.

Now there is a setting that allows me to specify that even if the PC is on battery power run the task. Also in my power settings I have enabled Allow Wakeup Events when running on battery.

But somehow the PC is not powered on automagically when the AC power is not connected. It does resume from hibernation when on charging. The battery is new so that should not be a problem.

Why is the PC not able to resume itself from hibernation when not connected to a power source?

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Check the BIOS settings. – Harry Johnston Sep 15 '11 at 3:44
i could not find anything useful in BIOS. Any suggestion on what to look for? – Rohit Banga Sep 15 '11 at 4:11

Waking from hibernation in Windows 7 apparently does not work too well when on battery.

Have a look at the freeware WakeupOnStandBy, which supposedly answers your needs, and might work better than the Windows scheduler.

If your computer has any power-configuration problems that impact on sleep/hibernate, Windows 7 has a utility to analyze such problems. See the article below on how to use the utility, and add the problems it finds to your post (or even better just upload the entire report somewhere and add the link to your post):
Evaluate System Energy Usage and Get Power Management Report with PowerCfg -Energy Switch in Windows 7.

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i could try that ... but what i am trying appears to be a basic functionality of windows. if it does not work then it is a major bug. does it not work for everyone else or is it is just because of my hardware or configuration? May be I have something configured incorrectly. – Rohit Banga Sep 18 '11 at 4:02
I have added a link for analyzing power sleep/hibernate problems. However, if this finds nothing, then Microsoft may just have decided on this as a "feature" (as distinct from "bug"). – harrymc Sep 18 '11 at 8:21
Thanks for that link. I ran the command. Somewhere in the report it mentions that the supported sleep states are S1,S3,S4. This ( suggests that the state I am looking for is S5, wake up allowed from clock etc. which is not listed in this report. Is this the problem? But the computer is able to wake up from hibernation when the battery is being charged. Why not when it is not being charged? – Rohit Banga Sep 18 '11 at 14:03
According to this link S4 is the correct state. I suggest trying WakeupOnStandBy as just another test, to see if your hardware is capable of waking up on battery. – harrymc Sep 18 '11 at 15:46
Also, better post the PowerCfg results. You could also try to Turn Off Hybrid Sleep in Windows 7, which is sometimes problematic. – harrymc Sep 18 '11 at 17:30

I'm guessing it may be doing sleep as opposed to standby, so:

Make sure hibernation is the only thing on. Go into the advanced power options and make sure "Turn off hard disk" is set to 0 (never), make sure under "sleep" the only things on are "hibernate after" and "Allow wake timers". After all that, it should be fine.

The difference between sleep, hibernate, and hybrid-sleep is where it stores the files and power consumption. Sleep stores your current working memory in the memory and still consumes power. Hibernate stores your current working memory on the hard drive and shuts off your power completely. Hybrid sleep does a little bit of both, storing it on both the memory AND hard drive, but keeping the computer on.

Alternatively, a laptop won't start if it has less than a certain amount of battery (which you can also set in power options). If it's less than a certain threshold, maybe it won't start regardless?

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My turn off hard disks option is set to 10 minutes. Under sleep options sleep after time is also set. The laptop is fully charged. Not able to figure out. – Rohit Banga Sep 15 '11 at 12:08
anyone has any idea on how to fix this? I really love the automatic resume from hibernate feature but at the same time do not want o leave the charger plugged in overnight for this? – Rohit Banga Sep 16 '11 at 5:46

Somebody from let me know that this problem occurs because of Windows Media Center, and this file can fix the problem:

It worked for me.

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