I cannot connect to the internet. I think I have my settings all out of whack now and need to get them back to the way they were when it was working. (I know my wireless router is working because my Dell has no problem connecting to the internet.)

Question

I cannot connect to the internet on my iMac through my wireless router. I think I screwed up the settings and need to reset them. I know the router is working because I can access the internet on my Dell laptop which is located right next to my Mac.

Answer 1

On your iMac try the following, in order, until (hopefully) resolved:
1a. Delete Preferred Network(s)
System Preferences > Network > Wi-Fi > Advanced > Wi-Fi tab
Under "Preferred Networks," delete the network(s) you regularly use from the list.
1b. Delete AirPort Keychain Entries
Launch the "Keychain Access" application located in Applications/Utilties.
In the windows on the left side: Select login for Keychains and "All Items" for Category.
Click on the "Kind" filter at the top, and look for any "AirPort network password" entries...and delete them.
1c. Add Preferred Network(s)
System Preferences > Network > Wi-Fi > Advanced > Wi-Fi tab
Add the preferred network(s) using the "+" button.
Restart or log out then back in.
2. Move System Configuration Files
(Note: You will have to reestablish your network connections settings.)
Go to /Library/Preferences
Move the SystemConfiguration folder to the desktop.
Restart your Mac. (Note: OS X will rebuild the files that are now sitting on your desktop. If this doesn't resolve the issue, you can move the folder back to it's original location.)