I have a laptop with an Intel Wireless Centrino 6300 module. Recently, the machine has stopped properly connecting to my wireless router. It will get stuck in a loop of connecting, then disconnecting and reconnecting. While connected, it will simply say "No Internet Access."
Running inSSIDer 2.0, it shows my network jumping around between two channels -- I know this isn't the case, because I've set my router to sit on one single channel. My MacBook Pro, Boxee Box, PS3, and Xbox 360 all connect fine to the wireless and have no problems at all.
I know it's not the wireless module, as I bought a second one recently assuming the first had died -- but I get the same behavior with both.
Sometimes, I can fix the issue temporarily by deleting the network (Using the Manage Wireless Networks page), and then re-adding it (via standard wireless methods). Then it will work for a few days.
But inevitably the problem comes back, and now the laptop simply won't connect to the wireless at all, even if I take steps that usually work.
Since I've ruled out the hardware, and it's unlikely some kind of interference issue (because I would expect to see it on any multitude of other devices), I would think at this point that it's a problem with Windows itself.
One thing that might be a hint, even though I delete the network, when I add it again, it's always listed as "Wireless Network Connection 2" even though there isn't another in the list.