iMac internet issues

1. Download OnyX (a free maintenance utility).
http://www.macupdate.com/info.php/id/11582

2. Open OnyX and Click Cancel on these two Alert Panels:
-Cancel the S.M.A.R.T. Box
-Cancel the Startup Volume Box

3. Enter your Password

4. Click on the Cleaning Tab

5. In each tab, execute the command. Check all the boxes in each tab. When its finished in that tab, it will ask you to reboot. Say NO. Go on to the next tab and repeat until all tabs are done. THEN REBOOT.

 

Have you at least tried to restart your router or check if all the settings on it are correct (via Airport Utility)?

The 2 machines that're using the same router, are they PHYSICALLY connected to the router or are the using Wi-Fi as well?

From the looks of it, it seems that there's a setting on your router that needs to be corrected.

1. Restart Router
2. If that doesn't work, check Airport Utility and verify that all your settings are correct (such as Radio Mode, Channel, Wireless Security, Access settings, etc.) then restart the router.
3. If that doesn't work, check the settings on your Mac. Sometimes Locations can have adverse effects on internet connections. Delete all Locations then create a fresh one. Make sure that all settings are correct. Automatic usually works best for the average user.

 

Try going into your system preferences under network. You should see a Location pull down menu. It should say Automatic if you have never changed it before, click it and then create a new location. Change any appropriate info you may need for your connection (most major ISPs are usable with the default settings) and then try your connection after that.