How to Find Out What's Keeping Your Computer from Going to Sleep
A lot of things can keep your computer from going to sleep, like downloading a file, opening a file on the network, or even a disconnected printer with an open job. Windows O/S have an easy method for finding out what the problem is.
In Windows Vista, 7:
1. Click Start Menu.
2. Type Cmd.exe, right click Cmd.exe, select Run as administrator.
In Windows 8, 8.1 and 10:
1. Press the Windows key + X keys.
2. Select Command Prompt (Admin).
In Windows XP:
1. Press to open Run box.
2. Type Cmd.exe, click OK button.
Within the Command Prompt type:
It'll let you know if anything is keeping the computer awake.