If you reformatted your Hard Drive you would have had to reinstall Office,
right?
The files that *used to be* on your HD are no longer there (at least not in
the same place even if you copied them back from another disk). Reformatting
erases the drive's content. Moreover, a freshly installed program has no
idea where or what they were anyway. The MRU will rebuild itself as you
start opening/creating files.
If this isn't on target, make sure you mention what version of
Word/Office/Windows plus a much more clear explanation of what you perceive
the problem to be.