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I have a problem where my Vista machine will not return from sleep or hibernation. This made me realize I have no idea of the mechanism involved. Searching has bought no results.

Could this be a corrupted registry? Or a problem with a file entry somewhere?

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You need to provide more details. Does the resume not boot? Does it crash? You some function not work? – dtech Jul 6 '11 at 18:20
    
Definitely sounds like hardware. Especially since the boot never gets to the OS in the first place. Does this happen everytime you turn off/sleep the computer? – surfasb Jul 6 '11 at 20:14

I cannot help with the specific problem right now, but to answer the general main question, "What is the mechanism that Windows machine 'knows' it is returning from sleep or hibernate?", I can answer that.

Computers use the "Advanced Configuration & Power Interface", which is a combination of computer hardware, firmware and driver software to handle power management, and that includes sleeping and hibernation.

http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface (of particular interest to your question is the section "Power States")

http://www.acpi.info/

Here in an in-depth guide regarding computer power management:

http://eetd.lbl.gov/EA/Reports/39466/

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For more on your specific problem, you will need to post more inforation about what it is doing, how it is acting, etc. – KCotreau Jul 6 '11 at 18:29
    
What occurs upon attempted resume is fan noise and cd drive noise. The laptop display remains off and no other keys/buttons are functional. The only thing I can do is hard power down. After perhaps 10-20 attempts to resume by powering down and retrying ( along with removing and reinserting the battery and other things I have no idea if helping or not) the computer eventually starts up- although it is usually a cold boot. – user72058 Jul 6 '11 at 18:41
    
These are always hard to say for sure, but it sure does sound like faulty hardware. Was it working, then all of a sudden, with no system changes (updates, etc.), it started doing this? You don't say who makes your system, but see if they have a hardware diagnostic tool and run it. – KCotreau Jul 6 '11 at 18:50
    
I've considered this could be a hardware issue, but what type would it be? The machine will cold and warm reboot flawlessly. This is the only issue I have with the machine. It is a Dell XPS1530 and it has passed their diagnostic suite with no issues. – user72058 Jul 6 '11 at 18:56
    
Well, you probably ruled hardware out if it passed their diagnostic. You definitely checked the memory? I might also consider downloading the Ultimate boot CD and run the memory tests on it too: ultimatebootcd.com/download.html. Sleep and hibernation modes are basically a method of storing what is currently in memory, so that is especially critical. So it happens both on sleep and hibernation? Did it work at one time? I would also make sure that I had all the latest drivers installed for your model. – KCotreau Jul 6 '11 at 19:02

The mechanism is called ACPI and theres already a good explanation of it on this thread, however your sleep problem may be your graphics card driver, download the latest driver from the graphics card manufacturer website eg www.nvidia.com , I'm guessing its a nvidia card. Ive had a few Dells and they don't always have the latest driver on their site.

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