Legacy Kernel Caller preventing sleep mode

Solution 1:

Thanks for all the suggestions!

Finally I narrowed down the problem simply by trial and error, disabling devices and rebooting. It was a TV card driver hung and not releasing the power request despite being no longer in use.

EDIT:

Unfortunately, the problem with TV card is intermittently recurring. Googling shows it's also quite common. I found that disallowing the driver from making power requests with

Powercfg -requestsoverride Driver "Legacy Kernel Caller" System

solves it.

"Legacy Kernel Caller" is translated on different Windows language versions. On my Polish system it says "Starszego typu obiekt wywołujący jądro".

Solution 2:

From the start menu, type in "Performance Information and Tools".

Click the Advanced Tools and click generate a System Health Report. It should point out legacy driver issues.

Edit:

Also try powercfg -request.