I recently was called to look at someone's aging laptop which had a number of viruses and other problems the most annoying of which was non functioning wireless which seemingly started at random. The wireless networking worked as far as finding and connecting to the network and even obtaining an IP address but would then refuse to transfer any traffic at all, local or internet and got the dreaded yellow warning triangle.
Initially I thought that the virus which I was in the process of clearing was the culprit or had corrupted the networking in some way. But after meticulously cleaning up the machine the wireless still didn't work despite everything I tried including latest drivers from Acer.
In the end I reasoned that the drivers or some part of the system was beyond repair and decided to back up and run a system recovery. Once complete everything seemed to be just fine, ran updates and installed software and restored the backed up items all fine and rebooted multiple times all sorted and ready to take back the following day.
Cue the next morning and I took the laptop back to its owner switched it on and the wireless had stopped working again and presenting the same symptoms as before.
After a lot of mucking about I eventually found via a couple of forum posts that there is a site with unofficial Atheros driver updates, which are newer then latest ones being given out by manufacturers.
The link below takes you to the download page. Use is obviously at your own risk but appears to work fine. As always make sure you have a backup of previous drivers and of any important data.
Extract the downloaded file then To install the driver go to device manager find the wireless adaptor, open the properties the driver tab the click update driver. Follow the prompts and select that you will choose the driver to install and navigate to the folder you extracted the driver to and select it. In my case a reboot wasn't necessary but might be worth doing anyway but as soon as it was installed everything was fine.
As far as I can see the cause of the problem is a windows update in last few weeks which breaks the current drivers. The site above also has updated drivers for windows 7 as well which solve similar issues on that platform.
If the above helps please post a comment to let me know.