Really need to have more info about your printer and how you've been using it and what you mean by not printing anymore.
What model is it?
Do the labels/media come out blank? or does it not do anything?
Does it have an error indication on the control panel? If so, what?
Are you normally using ribbons to print? or no ribbon?
Zebra's are pretty simple and easy machines to work with and fix.
If you normally use ribbons and the print is coming out blank now with a new ribbon installed, it may be that the ribbon is installed backwards from what it should be (usually with a different ribbon supplier or wrong ribbon ordered or shipped), try pulling it off the supply spindle and turn it over and try using the other side (it will only print from one side of the ribbon.)
If you don't normally use ribbons, but use direct thermal labels/media and you're not getting any print, then most probably you just put in new labels/media. In this case the labels/media is not direct thermal compatible and requires a ribbon (wrong labels ordered or shipped). You can test the labels/media to see if they are thermal sensitive by taking a hard object (fingernail or something else) and rub across the labels back and forth very firmly and see if if produces black marks. If it does, then it is thermal sensitive, if no marks, then requires a ribbon.
If it has an error indication on the front control panel, what is it? It could be that it needs to have a simple calibration run so that it is calibrated for the labels/media correctly. Maybe the labels/media or ribbon is not loaded correctly, double check the routing of each using the guide on the inside of the printer that shows the routing, or your user's manual. Depending on the model, sometimes the label/media sensor gets moved out of position and needs to be put back to it's normal position. Sometimes the sensor needs to be cleaned (depending on environment).
The internal configuration may have also been changed accidentally by someone or a software command and needs to be re-configured.
If you don't have any errors on the panel, no labels print out and the Data light does not come on or blink when you try to print, then you could have a communication problem with the computer. Double check your interface/data cable connections to make sure they are seated and secured properly. Check your printer port settings and printer configuration/customization driver settings.
Is there anything that was done to the computer (software additions, updates, changes, etc.) recently? What program are you using?
Most any fix required will usually only take a few minutes to do, but will need more detailed information about the problem.
List any additional info you can, or contact me about the details and we can see what it will take to fix.
Best of luck.