Unable To Join Homegroup

i have recently got a brand new machine and have updated from windows xp to windows 7. I have been trying to join the homegroup set up on my parents computer so i can access the printer. My computer is connected to my wired router before going into a ethernet connector in my wall and that then joins the modem. I am using norton internet security and so is my parents computer.

When my computer is plugged into the router and i go into 'trust control' in norton, my router shows up as full trust, but no other computers show up and when i try joining homegroups none show up. But when i plug my computer into the wall bypassing my router, norton shows all the computers on the network and lets me join the homegroup. So to summarise, i cant join homegroups when i am connected to my router, but i can join when i dont use the router.

Edit:
My router is a: Netgear WGR614v9