I am (and have been) having the same problem since Dec.29. The hours spent trying to figure it out have been enormous, as I thought it was a problem with internet, then wireless router, etc., etc. I was told by one tech. that when the wireless adapters quit working, they die a slow death. I am right now in the process of ordering a new one. If I go to the work of opening up the laptop (I have the SAME EXACT ONE you have - ASUS U56E) and it is loose or disconnected, great, but if not I want to have the right one to replace! Anyway - IF you haven't already figured this out - here is how you can get it to work TEMPORARILY until you replace it - REFER TO #7. ASUSTeK Computer Inc. -Support-
7. If wireless network adapter disappears from the device manager, please access BIOS by pressing < F2 > during boot up, press < F9 > to load the setup default, then press < F10 > save and restart.
This works for me, albiet sometimes I have to reboot a few times. There have also been new software/driver updates as of March 2013.
Hope this helps --