Line out and Line in sound driver for iMac (Yosemite)

I am trying to connect some older Altec Lansing Speakers I used with my previous iMac. The hook up was basic, but when I go to Sys. Prefs>Sound>Output (or Input) there is only Internal Built in, nothing else.
I got this iMac from my work. THE previous IT Admin guy had installed "Log Me In". I noticed various articles online about LMI screwing up peoples sound, so since I'm not using it I uninstalled it and deleted the driver from my Output and input in Sys. Prefs. since it apparently was doing nothing. Now, there is no other option/driver to select. I contacted Altec Lansing about trying to download a driver from them to use and they said since the company was purchased a few years back, they no longer offer support for these speakers. Does anyone know how I can fix this or where I can get the driver or a driver to use for "Line out" or "Line in"? Your help is appreciated.

By plugging in the external speakers contacts within the socket switch off the internal speakers and connect to the external. It isn't a software function, and speakers don't require drivers. You can check the audio socket is operating by plugging in earphones from and iPod, iPhone or any others. If they don't function you likely have a problem with the Mac.

You could try repeatedly pushing the speakers plug in and out multiple times then test again.

Thanks, Steve. Unfortunately it still doesn't work. Under System Prefs > Sound > Output there is NOTHING else to select other than the Internal Speakers. And I am unable to deselect that. Nothing happens when I plug in headphones either. The sound merely comes out thru Internal Built in speakers like before. Thanks for your effort/advice however. so perhaps my audio/headphone jack plug in my Mac just isn't working.

Based upon your test with the headphones it is likely your iMac has a faulty audio socket.

One way around this is to buy a USB audio adapter. In the past I have bought one off eBay for a few pounds. They have audio in and out sockets. These don't need a driver but will need selecting in system preferences, audio and output.

Which iMac model is it? Can you post some specs? All the iMacs I own have both an audio in and audio out. Are you sure you are plugging into the out or headphones and not the Audio In??