The jack of my external hard disk (Seagate 500GB) is faulty. Can I change it? If so can you please tell me how and where to get a replacement?
I agree with Dalsan. It's unlikely that you'll be able to get a USB jack that fits perfectly into the original Seagate enclosure. New enclosures on the other hand are easy to get and (usually) inexpensive. You will obviously need to get the correct enclosure (2.5 or 3.5 inch? IDE or SATA?) so check your drive before you buy. The only caveat is that some external drives use custom controllers (I know WD have a series which use neither IDE nor SATA), but again, you'll be able to ascertain this by opening the drive.
Not sure if you mean the power cord, the DC power input, the USB port, or USB cord. If it is the DC input or USB port, it would be cheaper and easier to just purchase an external drive case. Just make sure the case will fit your drive size (2.5 or 3.5 inch hard drive). Once you swap, there is nothing to set up, just plug in and go.