Most of those are pretty foolproof... They work or not.

See if you can borrow someone else's clip-on tuner (or use one of the many free online tuners and see if you can get the instrument in tune with that. Then check the onboard tuner for accuracy.
If neither is working for you, there may be a problem with the guitar's setup or intonation.
What specifically is the problem you're having?

Does it not come on at all? Does it come on but not display the correct notes? Etc