Lack of use is the most common reason print heads become clogged. When little or no printing takes place, the ink in the print head dries and clogs the ports. Most printers, including Lexmark, have a special print-head-cleaning program that can be run to clean the print heads. This program does not always do the job and even when it does it wastes a lot of expensive ink.
Turn off the printer and open the cover (it should lift on a hinge). Grab the printer cartridge and carefully pull it forward and up until it snaps out. You might need to remove more than one cartridge, depending on whether the black cartridge is clogged or if one or more of the colour cartridges is clogged.
Fill a small, shallow dish with 1/4 inch of warm water to which you have added two drops of dish soap and place your print cartridge(s), with the clogged print head down, into the water so that the head is soaking. Allow it to soak for overnight.
Remove the printer cartridge from the water after it has soaked overnight and carefully wipe the print head with a water-dampened swab. Inspect the print head. It should appear clean. If not, proceed to the next step.
Dump the water from the shallow dish and replace it with 91% rubbing alcohol. Set the print head in the alcohol and allow it to soak overnight. Remove the print head from the alcohol the next morning and gently wipe the head of the print cartridge with a swab which has been soaked in rubbing alcohol. Inspect the head. The head should appear clean.
Install the cartridge in the printer and print a colour picture. By the time the print head reaches the last third of the picture the print head should be printing perfectly. If your print head is still not printing properly it might be time to replace the cartridge.
Do not allow the alcohol to touch any of the rubber gaskets which might be present on the cartridge. Alcohol could cause these gaskets to dry and crack.