Here’s a solution that uses IFTTT. It just sends commands to an app running on your Windows computer. I use it to put my PC to sleep when I leave or go to bed, and it’s very fast.
You can’t use it to turn a PC on, though. As @denominator said, you’d need a wake-on-LAN function to do that, and I’m not sure if anyone has accomplished it here.
If you want confirmation that the PC is turned off, you can use the network binding to determine if the PC is connected to openHAB.
