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There are mixed findings/opinions and suggestions on this matter since the issue could be a result of a mixture of different issues, such as hardware settings, drivers, software settings and configurations, etc. Some of the solutions worked for others while not working for others. Some of the ideas discussed are:
1. If you let your PC sleep using a hardware button, then that same hardware button should be able to wake the PC up.
2. If you've allowed your PC to wake up through USB in the BIOS, then put your PC to sleep and then unplugged any USB device attached to it while it was sleeping, then that PC won't wake up unless the hardware power button is pressed. This could also be applicable to Bluetooth devices, since Bluetooth may be temporarily disconnected when the device goes to sleep.
3. If your PC had a custom manufacturer-specific software (e.g. Samsung Control Center) that allows the laptop (what device are you using, by the way?) to wake up when the lid is opened, then this feature was completely removed in Windows 10 brought about by the uninstallation of that software. You would need to re-install that software, run it in compatibility mode for a previous version of Windows and then re-enable the said feature.
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