Hello MagicFirend, and welcome to Seven Forums.
That may be the issue if the router is not set to allow the connected devices to see each other. If you open
Network Map, do you see the other computer listed when both computers are running Windows 7?
If not, then that is the issue with them not seeing each other. This must be resolved first.
If you do, then triple check through each item in the tutorial including the note and warning boxes at the top above the steps to see if there may be something that you missed. Next, leave the homegroup in both computers, and start over with creating the homegroup on one computer, and joining the homegroup with the other computer.
Hope this helps for now,
Shawn