Before you do anything else ....
if you can .... back up everything you can't live without while you can - before doing anything else (just in case)
when you do open the machine ... check both ends of the connector is not loose
also ... before you move any jumpers .... 2 questions
do you have more than one physical disc fitted?
if you do come back .... the re-jumpering needs to be done on both discs (master/slave)
is the connector cable either a 80/40 way ribbon? (which?)
with a 40 way c/sel won't work
do you have one of the new fangled SATA discs .... in which case don't move any jumpers.
disc read errors in my experience are generally down to either
loose cable
or a faulty drive (or a drive getting towards the end of it's life)
you could d/l and install thhe trial version of
http://www.hddlife.com/
it will tell you the status of the drive
either way .... it's easy to loose everything