no sound through headphones,previously no problem.

I would try updating your drivers

First I would try the obvious. Blow out the audio input with canned air, check your settings, restart the computer, reinstall/update drivers, factory reset the computer.

If all else fails, you may have to replace the audio jack. I haven't been able to locate any guides or replacement parts for this on iFixit so I would try to google it. If for whatever reason you aren't able to fix it yourself, then take it to a professional.