Can't I use it at work with headphone?

Almost all headphone jacks are standard male 3.5 mm input plug. That will plug into your phones female audio receptor

Just found this and it worked! Hope it does for you as well:
There should be a button on the DVD remote control with a headphone symbol on it. Make sure the headphones are turned on(red indicator on earpiece) and push the headphone button on remote. The headphones will only work in the back seats of the vehicle. Once you have audio to the headphones, you should be able to hit the AM/FM button on the radio and listen to the radio while back passengers use the headphones for video.

Did sound for a southern gospel group, using a yorkville powered mixer. Not familiar with your mixer, but, on the Yorkville I had an unused 1/4" line level output with the monitor mix on it. I bought a cigar-sized, 3-channel headphone amplifier / splitter from Radio Shack, called a Boosteroo. Has 1/8" stereo plug that I adapted to the mono output, with a 1/8" stereo to 1/4" mono adaptor. It receives the line level (monitor in our case) signal and supports up to qty 3 - 1/8" plug headphones. Battery operated. No volume control, so I added an inline dial (rheostat) volume control cable. Can't pull up on Radio Shack, now, but, found it available, elsewhere, online. Worked great for me!
Good Luck SdDude

Hello,

The volume control usually does not adjust the headphone volume just the speakers. Radio Shack carries an several types of inline volume controls that should work for you such as the following:

http://www.radioshack.com/product/index.jsp?productId=2102975

and

http://www.radioshack.com/product/index.jsp?productId=2272471

They carry them in stock at most stores.

I hope this helps you, if so please rate my solution.

BuddyMc

If it is still under warranty, take it back and get it replaced!!!!!!!!!

if you are not handy, then no.
repair will require disassembly of the ear piece, splicing of the wire, and reassembly.

radio shack

Here you are. Fix Ya?

http://www.1800customersupport.com/products.aspx?view=448&p=81&sc=13

May i know the model and the make of the product in details so that it can help me resolving the issue is a more prompt manner

i think its a factory setting you cant change. you cant listen to radio without headphones.