Why won't my Bluetooth mouse work with Windows 7?

I have a Targus Bluetooth mouse that I’ve been using in Vista for almost 2 years. Recently I upgraded to Windows 7, and now I’m having trouble connecting my mouse. My computer discovers it, and appears to successfully connect, but the mouse doesn’t work, and then it disappears from the Bluetooth devices list.

I’ve tried it on two other Windows 7 computers, and it didn’t work on those either. What am I doing wrong?

Also, in case it matters, I am using a Blutooth USB dongle.