It's best if only one person tries to find a fault and that nobody else touches the camera or sound gear while it's being checked - you are going to carry out detective work - so don't let anyone interfere with potential clues. Change one thing at a time and rerun the test to help pinpoint the problem
What description best fits your sound problem?
this is most probably a connection problem.
Start by checking that the headphones are plugged in properly. Hold the microphone and talk into it while you wiggle the headphone plug very gently. If this seems like the problem, find a way of taping the headphone plug so that it doesn't move around. This is important because the connections can work loose inside and it will soon not work at all.
If the headphones seem all right, carry on talking into the microphone while you check the cable where it leaves the mic, then at any joins in the cable and finally where it goes into the camera.
Hopefully you will have found the culprit and if it's a loose connection you can tape it up with some insulating tape. If you think it's a broken wire inside a cable you may have to replace that cable.
Go back over all your connections
Look at the levels if you have them, the meters should register in the middle of the scale. If everything is very low, you will need to turn up your levels and/or get the mic closer.
Have you looked to see if you can adjust any audio levels - either on the side of the camera or in a set-up menu? First find these and try turning them down - that includes the headphone level.
Or you might need to move the mic away from the sound a bit.
Headphones only 'monitor' the sound, if you turn down your headphone volume, it will sound quieter to YOU, but the CAMERA will still record at the same level
Make sure all connectors are plugged in properly. If you have any spare cables swap them over to find out if one of them is faulty.
If the camera has a switch saying 'mic/line' it should be switched to 'mic'.
Is your microphone cable passing near any mains cables or sockets? These can cause a lot of buzz on a cable. If you have to go close to a mains cable don't run your cable parallel but try to cross at right angles to it.
If all this fails it's probably faulty wiring somewhere. Before you blame your mic and cables, try to borrow another mic which you know works. If the problem persists with a different mic the fault is most probably in the camera and it will need to be repaired professionally.
If you've checked everything and you don't think the equipment's at fault, you may have to find out if your cables are screened and if not, get screened cables. Screened cables are designed to block outside interference and buzzes but they are not very compatible with home video equipment. A professional audio or music shop can help you with this.
If you have a hum or other interference which you can't get rid of, you may have to insert a Balanced converter into the cable before it gets to the camera. Speak to a knowledgable supplier for help on this.
If you are connecting something other than a microphone into the mic socket (e.g. a mixer, deck or amplifier) you will need to be able to select 'line' to make it work
You may have a camera designed for semi-professional use which allows you to select two types of audio input : mic or line. On the 'line' setting you would expect to hear nothing at all if you plugged a microphone in, and the mic should sound fine on the 'mic' setting. If it sounds loud and distorted on 'mic', try switching to 'line' : but try turning down audio level and volume controls first!