Solved set up a homegroup

Hi All,
I have setup a home group, but have a problem to fully implement it.
Here are the particulars:
3 laptops running windows 8 and they all can see each other and read and writeeach other’s files. 1 laptop is running windows 7 Home Premium. This also cansee and write to the other laptops. All laptops are connected via Wi-Fi to arouter.
The last computer is my desk top. It is connected via Ethernet cable to therouter. This one is running windows 7 ultimate. This one is not seen by any ofthe laptops, because I cannot join the network.
I click on join and it asks for the password, after typing the password, itstarts something. I can see the progress bar moving, but it will not join thenetwork. At the end of this I get a message: Windows cannot setup a Home groupon this computer.
I have no idea on what to do here. Sometimes it tells me that there is a home groupavailable, and sometimes it does not. Could this be my router?
Thanks for your help
Sven

Update:
it appears that I have a broken router. I installed a wireless adaptor in my desktop and now I can log on to the other computers. for some reason the wired connection will not allow me to connect to the other computer. I will mark this Solved
Sven