I recently changed my motherboard. But I didn't reinstall Windows. Now my system refuse go to sleep/hibernate. When it put to those modes the system automatically comes back to the login screen. It worked fine before the MB replacement. What's wrong with this and how can I fix this?
Have a look in device manager & make sure there are no devices missing drivers or not starting. If something has a bang or missing drivers then that could prevent sleep/hibernate...
There are 3 options there. Auto, S1 and S3. I changed it from Auto to S3 but system still wakes up automatically. I even flashed the BIOS to the latest version.
Open up device manager, select something that could wake the PC, go to the power managment tab and unselect "Allow this device to wake the computer". If your PC can then sleep correctly then you would of found the culprate. You've not said if you've reinstalled Windows after you've changed your motherboard. That's something that's always recommended as some drivers may not be configured correctly, so I'd suggest that you backup your data and reinstall Windows. You'll then want to try sleeping/hibernating before you activate Windows 7 or install anything.
What should I look for? I used this command, Code: powercfg -devicequery wake_armed to find the devices that wake up the PC. Then as you said I disabled their ability to wake up from Device Manager. Even after that command shows nothing, the problem remains. Yup. You're right. I didn't reinstall Windows after the MB replacement. Seems like this should be the case. I'm gonna do it as you said. Thank you.
sfc /scannow checks for corrupted system files and refreshes them. (But it appears you are reinstalling - the longest road, but the safest bet)