I used wifi at home in the morning, with no problem. I used ethernet during the day at work. When I got home, wifi wasn't working. At first, it was still an option in the Network tab of System Preferences (along with Ethernet, Firewire & Bluetooth PAN). When I clicked on 'Assist Me,' and started the process, I wasn't able to give the information needed. When I clicked 'Go Back' until I got to the main Network screen, the 'WiFi' option was no longer present. It is also not an option with I click on the "+" button to add a network option. In addition, on the top bar, the WiFi icon is greyed out, with an 'X' in it. Clicking on it shows: "WiFi: No Hardware Installed." To add to the fun, when I called Apple Support, he had some resets in mind to try, but my computer will not stay off. Clicking 'Shut Down,' turns it off, but then right back on. Holding the power button turns it off, but he had me unplug the power for a minute, then plug it back in. When I do plug back in, it restarts again, on its own. Any help would be greatly appreciated... Thanks!