If that doesn’t fix it then your telescope’s collimation may be off. That’s not as easy to correct because it involves re-aligning the mirror (in reflectors and cassegrains) and knowing how to tell when it is spot-on. There is something called a “star test” that can check for collimation. Refractor lenses rarely get knocked out of collimation after the scope has been completely assembled. But they aren’t always perfectly aligned to begin with, and once constructed it is horribly difficult to adjust the lens.

It’s also possible that your eyepiece is screwed up mechanically; if one of the lenses comes loose or a part falls out then you’ll be in trouble. Try another eyepiece to see if it works better.

If none of your eyepieces are able to focus at all and you don’t suspect a collimation problem then it may be that your telescope’s focal point doesn’t occur in the same spot where the eyepiece is put. If the scope is “farsighted” you can attain focus by buying a longer focusing tube that will put the eyepiece further back. If it’s “nearsighted” and the focus is inside the telescope tube, then you are pretty much S.O.L.