on plugging the headphone in inspiron1525 i m able to hear only the background sound nothin else.... what s the problem??

whenever i plug in headphones in my dell inspiron1525 with xp OS, i m able to hear only the background sound and nothin else. but if i insert headphone midway then only i m able to hear the entire sound. can anyone suggest me what the problem is? is it with the lap or the headphone???????