I'm running Kubuntu 12.04 on an HP Compaq nc6320 with an intel wireless card. This has worked well for quite a while. While on an extended trip, the wifi quit working - I could not get an IP address from the wifi hotspots anywhere. When I found a motel with a wired ethernet connection, I was able to do a system update and the wifi started working again. I don't know which update was responsible.
Later, the wifi quit working again. This time, the blue wifi light would not come on. This was new. When I got home, I swapped out the wifi card with one from another computer, but same thing. I then put in a PCMCIA wifi adapter (D-Link DWL-G630) and it would still not work.
Strangely enough, I can boot up any variation of Linux from a flash drive and the wifi adapter works automatically, so it's apparently not the hardware. But when I go back to the Kubuntu lspci shows no onboard wifi card, though there is one, and there is no wlan0 to be found on the system - only wlan1 for the adapter.
Anybody have any suggestions?
After much grasping at straws, it turns out that the wireless was disabled somehow. It finally recognized the wireless adaptors but wouldn't let them work. the command "sudo lshw -C network" showed "-network DISABLED". This even happened to the external adaptor that I added. I have no idea what caused it.
It turns out the solution was "sudo rfkill unblock all" to enable all internal switches - at least for now. In order to keep this short, I'll just refer you to the rfkill man page.