There are a couple of things you could do. You could try opening the case, finding the socket and plugging the jacl into it. This way should be able to see if the jack has made full contact. If not, you could try moving the connectors manually (I don't recommend this if you don't know what you are doing). As I mentioned earlier, you will be dealing with extremely soft metal - so be very careful not to move it too much as this could break it.
If you know how to fit components like these to your system, then you could look at buying a new one.
If you are unsure how to do any of the above, then I would suggest taking it to a specialist.
Please bear in mind, these are just 'best guesses'. I deal with audio equipment more than I do computers and find usually this is the case - but not always.