Max P. Tafferty found out how to easily reconnect a wireless Bluetooth headset to your Windows 8 computer:

1. turn on your bluetooth device
2. right click the volume icon in the taskbar
3. select “playback devices”
4. right click your disconnected device in this list
5. click “connect”
6. (optional) if your computer doesn’t immediately switch from speakers to headphones, select them and hit the “set default” button at the bottom of the playback devices window.

Source: http://mprtech.tumblr.com/post/64311745286/reconnect-bluetooth-headphones-in-windows-8-the-easy