Hi Rajesh
Hopefully you have already got this sorted, but in case not I have had the
same problem and tried the VBE solution suggested in other threads, but it
did not work. In frustration I carried on clicking the hide and show field
list button and noticed a line appearing in the right hand corner of my
screen each time I clicked to show the field list. This line was actually the
field list box, which had virtually disappeared off the screen (I think due
to changing screen resolution when switching between using laptop screen and
a monitor). I clicked on the line and was able to drag the field list back on
to the screen.
Don't know if you have had the same problem, but thought I would write in
case it helps.
If it doesn't then you can always change the fields using the layout button
contained with the pivot table wizard dialogue box.