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Is there a tool or method to find out, what prevents Windows Vista 32 bit from entering the standby mode? My home pc is set to standby after a certain time of inactivity. But quite often it just stays awake and I have know idea why. I know of things that will keep it awake and already checked devices and network to no avail. I suspect there is some application or service that tells the os to stay active and I hope there is some tool to find the culprit.

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Any 3rd party driver or program running in the background can cause this. I use msconfig to start disabling startup programs and restart the PC to see if it sleeps now. – Moab Sep 24 '12 at 21:53
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Also check your devices in the device manager, right click=> properties =>power management=> "allow this device to wake up the computer". In my case, disabling that for a USB mouse fixed this. – terdon Sep 24 '12 at 21:57
up vote 4 down vote accepted

Right click CMD and run as Administrator. Enter powercfg -requests

If you are lucky, it may indicate a driver preventing sleep.

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thanks, great! I also found pwrtest.exe from the Windows Driver Development Kit, but powercfg does not need to be installed. – Arne Sep 25 '12 at 14:40
    
In my case, I had external audio amplifiers plugged into two different computers. powercfg -requests indicated the audio driver was preventing the computer from entering sleep. I used powercfg -REQUESTSOVERRIDE DRIVER "driver name" SYSTEM to override this. See jasonhartman.net/2012/06/…, which is very helpful – Dan Halbert Aug 9 '14 at 23:55

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