Windows 7: Problem with wireless adapter or access point

I'm using HP pavilion dv6-3085tx laptop. It has Windows 7 home basic 64 bit operating system and Atheros AR9285 wireless network adapter.

From past few days, After servicing of laptop, Laptop shows the wireless network (good or excellent strength) but windows can't connect to network and gives error that there is problem with wireless adapter or access point.
The laptop connects to network only when it is within 3-4 feet from the Wi-Fi Router (Beetel 450TC1 Wi-Fi Router) or via LAN cable.

This same laptop was working fine earlier since last 18 months, even from the distance of more than 20-30 feets. Also other laptops (hp, sony,dell etc.) and mobiles are working absolutely fine with same Wi-Fi router as usual.

Then I tried every possible troubleshoot methods and actions which are available on HP site or on Google to solve this problem. Like reinstalling drivers, Updating BIOS, Windows Reinstalling and then finally Factory Reset of the system. But still the problem persists.

My wifi Router settings are also correct and there is no filtering enabled. Then I changed my router channel to different channel from others' router, but of no use.



Please help me to solve this problem. Thanks in advance.