900 firmware error on Lexmark x204n

Normally when you get a firmware error, it is usually because of a failed attempt to install a firmware update. Often when this happens the printer is useless. Were you trying to install a firmware update for the printer? How is the printer connected, is it connected via usb cable or via network, or parallel cable? You can try to download the most recent firmware for this printer and try to update the printer again, you need to make sure that any firmware update is not interurpted. Try turning off the printer, unplug the printer power cord then turn on the printer for a 10 seconds, turn off printer, plug in the power cord then turn on the printer and see if you still get the same error, if you do try to update the firmware, if you can not update the firmware it looks like there may not be anything you can do, except send it out for repairs. If the printer is not worth the cost of sending it out for repairs you may need to just replace the printer.