Atheros Wifi adapter doesn't work with "n" router

[nusha]

Hello
I have an HP pavillion desktop (s5360f) with Atheros 802.11 a/b/g/n Dualband Wireless Module and D-Link router DIR-615. My numerous Laptops and iPhons / iPads work fine, but this desktop which is further away from the router (in another room, about 20 meters) only shows 1-2 bars of wifi. First I bought a big additional D-Link antenna (7Ghz) but it didn't really help - sometimes connction shows 3 bars. I was told this antenna should help a lot. Then I checked with my router settings and saw that the HP uses "g" connection when everything else uses "n". I even set it to only use "n" but still it shows the HP using "g". I updated the driver (Atheros 9.2.0.113 for AR5B91), but it didn't help. I have "n" enabled in Atheros in Device manager.
Now I'm lost and can't think of anything else that can be a problem and / or how to fix it... I don't have any thick walls between the router and the HP, my iPhone seems to work in this room just fine...
Please help!
THANK YOU!

 

[WebMattR]

Out of curoisity, are you suffering any symptoms of lack of signal qualities (glitchy video/slow connectivity)?

And what speed does the HP Desktop show it being connected at?

 

[nusha]

Thank you for your fast response!
Yes, when it shows 1-2 bars surfing the web is normally a little slow on it's own but when I'm downloading something at the same time - almost impossible. I never have this with other computers. I actually just checked with my laptop at the same location, same OS, wifi settings but Atheros AR9285 - has great connection, uses "n".
I'm not sure how to check for speed... when I open Network and Sharing Center and look at wifi properties it shows 130 Mbps (yeah, right!), Vistumbler shows 25-40% signal. Is that what you were asking about?

 

[WebMattR]

Well, here's my quick fix/problem locator tip: buy yourself a little usb wireless dongle. Plug it in, set it up (you can get them for only like $20), and see what it sees.