Having the Airport connection on your Mac suddenly stop working can be a frustrating experience. While such drop-outs can usually be attributed to an improper Wi-Fi configuration or an incompatibility with a router, sometimes it can happen if there are faults in the Wi-Fi hardware itself.
Generally software configuration problems result in dropped connections, the Wi-Fi services constantly attempting to join other networks, or having connection timeouts when you select a network to join. In the case of a hardware fault, while in some instances you might have trouble maintaining a Wi-Fi signal, you might also see the Wi-Fi connection menu indicate that Wi-Fi is turned off. If you then click the menu it will show a single grayed-out option that states "Wi-Fi: no hardware installed."
In these instances, there are several potential issues that could be occurring, including a loose antenna, corruption in some system hardware variables, a loose Wi-Fi card, or a broken Wi-Fi card.
To get to the root of the problem, the first step is to determine if the problem is truly because of a hardware malfunction, so try booting to an OS X installation DVD or to the Lion Recovery HD partition to check the Wi-Fi functionality. Doing this will bypass the main operating systems and offer a generic boot environment that should properly recognize the Wi-Fi hardware in the system. If the hardware appears to work in this environment and not when you boot to your main operating system, then the issue is likely not a hardware fault, but if it still does not recognize the hardware, then it is likely there is a hardware fault.
Another thing to keep in mind at this point is the system might still recognize the hardware properly but still have hardware faults that contribute to dropped connections, such as if an antenna is loose or broken. Therefore, try moving the system, gently tapping or shaking it, and closing its lid (for laptops) in the alternate boot environment to see if you can induce a Wi-Fi dropout from these actions. If so, then this indicates the possibility of a loose connection that could be contributing to the problem.
Beyond antennas, to further confirm a hardware malfunction you can try running the Apple Hardware Test suite on your system by rebooting with the D key held down (if your system came with a gray restore DVD, then you may need to insert that to load the hardware tests). For newer Macs you may need to use an internet-based version of the hardware tests by holding Option-D instead; however, given that the problem at hand is a Wi-Fi error you will need to use a physical Ethernet connection instead.
When the hardware tests are run, check its output for an error code that contains something like "4AIR" with a bunch of numbers and slashes behind it, such as "4AIR/1/40000002:0x7ea93a4." This output indicates the tests have indeed found a problem with the airport controller.
If you are able to confirm the problem is from a hardware-based fault by these procedures, then you can better determine how to handle the problem.
- Antenna problems
If you can induce a Wi-Fi drop-out by moving, tapping, or shaking the system, then it is likely you have a problem with your Wi-Fi antenna. In laptop systems the antenna connects to the motherboard but travels up into the screen, so it moves with the hinge and therefore has the possibility of being dislodged when the screen's position is adjusted. If the antenna is broken or loose, then it will greatly limit the system's ability to maintain a Wi-Fi connection.
To correct these antenna problems, the system will need to be opened so the antenna and its connections can be examined. If your system is under warranty, then be sure to have this done at an Apple store or another authorized Apple service center; if not, then you can try doing this yourself by referencing a clear take-apart manual such as those offered by iFixIt. Once open, check the antenna for any breaks, especially where it enters the hinge area of laptop systems, and tighten it down if the connection screw to the Wi-Fi card is loose.
- Hardware configuration issues
If antennas do not appear to be the issue, then first thing you can do is reset the system's PRAM (parameter RAM that holds hardware configuration options) and SMC (the system's power management controller) to clear corruption in hardware variables that might impede on the system's ability to properly recognize or manage the Wi-Fi module. Apple has knowledge-base articles that cover how to reset the PRAM and how to reset the SMC.
- Wi-Fi module connections
Beyond resetting hardware variables, one potential issue is if the Wi-Fi card has become dislodged from its connection on the motherboard, which can happen if a system is dropped or otherwise jarred. To help test this option out, since on many systems both Bluetooth and Wi-Fi are on the same card, try enabling and using Bluetooth features to see if they work. If they also show errors, then this is a good indication that the card is not working properly, but do not rely on this as a full diagnostic because in some systems Apple uses separate cards for Wi-Fi and Bluetooth. In these cases the Bluetooth connections might be doing just fine, even if Wi-Fi is not working.
To correct a faulty Wi-Fi module's connections, as with the antenna you will need to open the system up to access the card, which should only be done if the system is not under warranty. Using instructions from iFixIt, remove the Wi-Fi card from the system and use compressed air to clean both the card's contacts and the contacts in the motherboard slot. Then re-seat the card into its slot and secure it, followed by restarting the system to try again. If this clears the problem then the system will likely display a message about the new hardware that was found.
If the problem persists after clearing the card's contacts and reseating it, then it is likely the Wi-Fi card itself or some component of the system that interacts with it is broken and needs to be replaced. At this point, you can either purchase replacement cards from iFixIt and other places online and install them yourself, or have the system serviced by an Apple technician.