How do I set up iTunes Home Sharing?

I would like some songs my sister was able to receive from her boy friend's computer. It was able to receive a few on my computer until her computer ended up downloading another version of Windows 7 and shutting down.

It will work just fine to home share with my Dad's computer, but it just doesn't recognize my sister's computer. All three of us have Windows 7. I have searched for and tried suggestions like:

1. File>Home Sharing>Turn Home Sharing On. In fact, it even says it's turned on with my sister's computer, but neither my computer or my Dad's computer recognize it.

2. Try to close down and reopen things.

3. See if Bonjour is working:

Nothing is working.