My AC adapter wont fit into the DC jack. Can I repair this myself?

I've seen that you can buy a new DC jack for my Sony VAIO laptop (pcg-791m/vgnfs115z) on ebay, and have considered trying to fix it myself, but I am unsure whether this is the best option.
I don't want to get ripped off if I take it into a laptop repair centre.
I have bought a new AC adapter to see if the problem was that, but that was still loose in the socket.

Zoe J
July 2009