I know this is a very late reply but it might be helpfull to some one else,
You can get the firmware updates from Lexmark at the below address
support.lexmark.com /printerfirmware/
you will need an authorisation code to access it which is realted directly to the model of printer you need which Lexmark will give you, the point of the code is to prevent pwople downloading the wrong firmware and scrappping their printers.
From what i have found this only works if the firmware is only slightly messed up, if the printer requires a full firmware reload you will probibly have to get another controller card or take it in to Lexmark especially if it is a usb printer.
If it is a an ltp1 printer go into command prompt and type the following
copy /b filename.pjl lpt1
you might have to do it twice with a second file with the extension .fls.
Hope this helps