Vista wireless only works when Windows 7 PC is on

Hi.

I live in an apartment/house where we just got internet. I installed everything, bought a Linksys WRT160-N, installed dd-wrt on it. I have 7, wireless works perfectly. Guy above me has XP - wireless works perfectly.

Friend has Vista who lives kitty-corner to me - doesn't seem to work. Gets signal (good strength) but always "limited connectivity" and doesn't complete connection. I did a lot of experimenting and here are some of the results of the experimenting.

Turned off/disabled homegroup - did not fix.
BG/N stuff is fine - everything matches up. He's got a "hacked" version of Vista if that matters and a Broadcom wireless card (Atheros HDA modem).
Drivers are up to date.

I had vista diagnose the problem and did a repair by acquiring IP settings. This seemed to work ..sometimes..when I turned off ipV6. But hasn't been consistent. I turned off iPv6 but the Vista seems to keep turning it back on (haven't tried full disable yet). Another thing in the wireless settings that is perpetually checked and needed is the Enable WAN settings. This option is not even present in 7.

His firewall? I uninstalled all the anti-virus software so only windows firewall is on. Weirdly enough, in the windows security center it gives a note about "two firewalls can cause conflicts" even though only the windows one is on. Couldn't figure that out. Friend says it could be windows defender.

Wireless security key settings are matched up.

Here's a kicker. His wireless magically works like perfect when my wireless is on. He lost connection when i turned off my computer or just turned off the my wireless switch. This happens whether I am close to his computer or farther away.

Differential diagnosis? I think it might be router interference. There are a lot of wireless connections floating around our building. He connects to other networks in the area without problem even though they might be further away in different buildings (he's on the second floor). My router is on the floor on the first floor. I'm going to move it around and see what happens. But I didn't think that explained the fact that his wireless worked only when mine was on.

Earlier in this whole process I tried changing the channel to 11 and that seemed to mess everything up. Even my computer didn't get connection for some reason even after I restarted the router.

Any and all help is appreciated. Thank you.

 

Moved my router around to a better place. This worked for a day and a half, surprisingly. Then it stopped. I changed the channel on the router from 6 to 1. No luck.

I changed both our workgroup names. I checked his computer and he wasn't set to connect to anything (I checked this through the Internet Options LAN settings) for ICS. I looked at my options and turned off anything ICS related. Nothing so far.

 

I left for the weekend but my neighbor's internet was working because my other neighbor upstairs was using the internet at the time. So it seems to be connecting or it seems to be sharing the signal? Anyone hear of this before?