Problem "seeing" other computers, but not with getting online?

OK, so before I say anything let me just say I've power cycled countless times, reset the router to factory defaults, and even upgraded the firmware. And the router I have is a dlink wbr-2310

http://www.dlink.ca/products/?tab= [...] v=WBR-2310

So here is my setup: My internet connection comes in through cable, and first reaches my modem. My modem then connects to my router, which splits the connection to my main computer (wired) and my laptop (wireless). Both can easily and properly connect to the internet with high speeds. However my laptop cannot see my main computer. My main computer can see and access the files of my laptop. Both are running vista. When I hover my mouse over the internet connection at the bottom right of my screen on my laptop, it always says that it is identifying. And then it is properly connected for about 1 second, and goes back to identifying. I think the reason why I can't see my other pc is because when it is identifying, vista sets the network as 'public'. Once it connects, it is set to 'private' and I can see my main computer, but then it's gone again, because it is identifying. Everything used to work perfectly. It was sort of sudden. Do you know what's wrong?

PS: My laptop is identifying and the signal strength is supposedly 'low' but I am 15 feet away from it, and the doors are left wide open. Other than that, the walls are just wood and drywall, no wires or metal or anything. Please help me, I don't know what's wrong. Thanks in advance.