Cannot load a wepage, but Router shows connected.

I have two desktops, a laptop, a PS3, and an Xbox 360 connected to my router. For the past 3 months the internet has been going in and out intermittently. I originally thought the radius of the wireless signal (a Linksys wireless-G WRT54GL) was dying as I was losing the connection to the PS3, laptop, and my personal desktop that were using wireless cards. I replaced the Router with a brand new Belkin Play wireless-N router. The modem has been replaced three times by Brighthouse, each time with a brand new modem, and Brighthouse has confirmed that the modem is running properly. The devices connected to the router are as follows:

Desktop A running Windows 7 64bit (wired, but with a wireless capability)
Desktop B running Windows Vista (wired)
Laptop A running windows 7 32bit (wireless)
PS3 A (wireless)
Xbox 360 A (wired)

I have disabled and enabled the firewalls and tried every combination between the three computers and the problem persists.

A couple interesting things do happen. The router will show that the internet is connected but will be unable to load a webpage, yet the LAN on Desktop A states there is no internet connection. For some weird reason though, while I was unable to load a webpage, World of Warcraft ran fine (unsure if this is related). I have heard rumors that Windows 7 and Windows Vista are uncompatible when networked together, but have not found any substantial evidence.

If someone could please help that would be awesome.