Reinstalling LW shouldn't have affected your library unless it was located in the program folder. If you can't find them using the search function(Start>Search), then possibly they were accidentally deleted?..........It happens.
http://www.gnutellaforums.com/open-d...ry-advice.html
The only other thing i can think of is a virus. Some will remove your files.
http://www.gnutellaforums.com/open-d...uld-aware.html