Sorry to be picky but would suggest -
1.  ensure that there is an extra connector on the ribbon cable linking the
drive to the mother board AND a power cable.  (If not this can be resolved)

2. make sure that you've set the jumper settings on the new drive to act as
slave (should be a diagram on the drive or the manual)  (It is damned hard
to see let alone to do this once the hard disk is screwed down)

3. attach the ribbon connector to the slave (end connection) and the master
(mid connectior) and then attach a spare power lead. (The red line on the
data cable looking towards the red lead on the power).  (It's disheartening
to screw it down to find that the master / slave setting wasn't set or that
the HDD is duff so test it first)

4. make sure that the (loose) hard disk is not touching anything
electrically

5. power up and the computer will either see the new hard disk drive or you
will have to go into CMOS settings.

6. if successful carefully unplug the hard disk drive, screw it down,
connect up again and close the lid / side.

Regards.

Bill Ridgeway
Computer Solutions