So I'll summarize. In short when this happens you want to turn off the computer that hosts the homegroup so you can create one on the PC that will always be on.

Here's a link (one of hundreds) about this.
http://lachlanmiskin.com/blog/2012/10/01/create-new-windows-homegroup-when-there-is-an-exisiting-homegroup-on-the-network/

And the hundred others:
https://www.google.com/search?q=create-new-windows-homegroup-when-there-is-an-exisiting-homegroup-on-the-network&ie=utf-8&oe=utf-8#q=create-new-windows-homegroup-when-there-is-an-existing-homegroup-on-the-network