The best I can suggest it to try the drivers that can be downloaded from here: LINK These drivers say they're for Mac OS X 10.1 and higher. (Maybe you already have them?)
Make sure the USB cable is plugged in, go to Print & Fax in System Preferences, and then click on the small + sign at the bottom of the dialog box. Your printer should be detected.
Be aware as a long time Lexmark user they do not have fully compatible drivers for OS X.4 Tiger and you cannot access utilities, Leopard worked quite well with the Lexmark All In One. However if you are using Snow Leopard just will not work pure and simple. Despite this for the last five or six years the Lexmark web site continues to sprout the 'Mac Compatible' message, however driver is still version 1 or 1.1 which was released for Jaguar OS X.2 and it is so frustrating as all their IT 'professionals' are based in india it seems and simply updated the web site to say OS X.? compatible and do no work on updating drivers.
Simply threw mine out and got an Epson compatible with Snow Leopard.
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