It happened to my new Dell laptop twice also. The first time, I uninstall and reinstall the driver using the Driver CD and it worked. The second time, I did 'system restore' and it worked also.
You can try either one. I'm not sure what happened but in my case only happened to my Dell laptop. It just suddenly lost connection to the wifi adapter.
My laptop's (windows vista) battery is depleted, so I always use the power cord. The wireless connection was fine. After I returned from vacation, I opened the laptop & found the wireless connection is lost due to the "lack of network adapter" (the computer can not detect any wireless adapter). I went to the device manager and found the wireless adapter is "fine & in working condition". I restarted the computer and the problem is still there.
Can anyone tell me what to do?
Thank you so much in advance,