my imac doesnot recognize my wifi

Are you talking about the internal wireless card of the mac.. often apple referred to as Airport.. or are you talking about a router.. which apple still refer to as Airport.. you can see our problem.. there are airports everywhere.. but none of them have your plane..

So if this is internal airport.

If you upgraded (so called) to Yosemite this is common..

What model and year iMac? What OS (as most people forget to update their profile.. 10.6.3 is unlikely).

Do hardware test and see if the wireless is still there and working.

Reset the PRAM and reboot the computer.

If this is external, an airport router.

What model is it?

The usual procedure is press and hold reset until front LED flashes and redo the setup.

Ensure you have ipv6 set to link-local only in the computer network, whether wireless or ethernet.

Redo the setup via the airport utility.. if that has issues tell us exactly what issues.

Try the basics first:

Change your router channel number. Most times this works & is all you have to do.

Disconnect & reconnect your modem. unplug it for about 10 seconds. Plug it back in. Do the same for Apple’s routers. Wait for everything to reboot.

System Preferences>Network

Click the Assist Me button.

In the next window that pops up, click the Diagnostic button & do the necessary.

Research Knowledge Base for network problems that pertain to the OS that is currently installed on your computer. See these basic networking KB Articles: http://support.apple.com/kb/HT1401 AirPort troubleshooting guide

http://support.apple.com/kb/HT4628
Wi-Fi: How to troubleshoot Wi-Fi connectivity

http://support.apple.com/kb/HT2712 Using network locations in Mac OS X

Manually provided DNS server addresses are higher priority than DHCP's

http://support.apple.com/kb/HT1714 Solutions for connecting to the Internet, setting up a small network, and troubleshooting

============================

What to do when you can't connect to the Internet

Also, run the Airport Utility app which is located inside the Utilities folder.

=====================

If using a Linksys router, contact LinkSys Customer Support and/or post in their forums.

If using Apple's Airport, please re-post over in one of the AirPort Forums.

Mac OS X (10.6.3)

Use the combo update to update to OS 10.6.8. Repair permissions & restart your comp when done.