Wired computer doesn't see wireless computers on network -cannot join

I recently replaced my wireless router and Bellsouth DSL modem with a single Netgear DGN2200 DSL modem/wireless router. The problem is my desktop which is wired, cannot see the laptop computers that are on the network via wireless connection. If I start a homegroup with one of the laptops, the other laptop can join but my desktop cannot (no "join now" option). If I start a homegroup with my wired desktop, neither laptop sees it.

However, if I connect my desktop to the network using my USB wireless adapter, then I can establish a homegroup with either a laptop or the desktop with no problem.

I have checked that IPv6 is enabled and that all the services listed in other posts are enabled. I'm fairly certain the cause is some setting in my router security, but I don't see anything that would prevent my desktop from linking. I can also get on the internet with no problem.

Please help!