Q: my macbook pro cant detect my wifi anymore?

First contact your ISP.  You need to confirm that the issue is not on their end.

Change your router channel.  Sometimes this is all you will have to do.

Power cycling the router.  Read the router's user manual or contact their tech support for instructions.

System Preferences/Internet & Network/Network

Unlock the padlock

Locations:  Automatic

Highlight Airport

Click the Assist Me button

In the popup window click the Diagnostic button.

System Preferences/Network- Unlock padlock.  Highlight Airport.  Network Name-select your name.  Click on the Advanced button.  Airport/Preferred Networks-delete all that is not your network.

Place a check mark next to "Remember networks this computer has joined."  Click the OK button and lock the padlock.  Restart your computer.

http://support.apple.com/kb/TS1920 Mac OS: How to release and renew a DHCP lease

No internet connection (wireless)

Check to see if an extra entry is present in the DNS Tab for your wireless connection (System Preferences/Network/Airport/Advanced/DNS).

Delete all extra entries that you find.

Place a check mark next to "Remember networks this computer has joined."

Other resources to check into:

Non-responsive DNS server or invalid DNS configuration can cause long delay before webpages load

Netspot

How to diagnose and resolve Wi-Fi slow-downs

Pv6 troubleshooting

What Affects Wireless Internet?

Solutions for connecting to the Internet, setting up a small network, and troubleshooting

If using one of Apple's Airport routers, read its user manual or post in its forum area. If using a 3rd party router, read its user manual, contact their tech support department/website or post in its forum area.

Power cycle the router anyway, even if other devices can or are connected to it.

OK. This has happened to me a few times in a couple of years: (Model: MBP 2011)

Here's what worked for me:

Note: You can do this from another device that DOES connect to your home wifi (iPhone, PC, ..etc) or you can plug in your MBP to your router via an Ethernet cable.

1- Log in to your router configuration panel by typing 192.168.1.1 into your browser (The Username and password are usually supplied by ISP or manufacturer). You can google it as well.

2- Go into "Home Network" Section and then "Devices" Subsection. Click on Edit somewhere on your screen (Mine is on top right corner. I have a Thompson router). Delete the Wifi MAC address of your MBP. If you don't know which one it is or don't know what a MAC address is, delete all devices you see there. (don't worry, this is like tapping -forget this network on your iphone-)

3-Click Apply

4- Go into "Home Network" again. Look for "Channel" line. It should be on "Auto". Change it to a random channel like 3, 4, 5 ... Click Apply. Change it again to "Auto" click Apply again.

Your network should be detected right away by your MBP. If not, restart your router (turn off, unplug about 30 sec and plug back in, turn on).

It's possible that the WiFi 'channel' option in your router configuration/administration panel is set to 'Auto' and it went to a channel above 11, which seems to cause a lot of MacBook Pro users a problem.

So try changing the WiFi 'channel' to 11 or lower, and see if that helps - seems to have solved my problems!