It sounds as though, rather than a Windows reinstallation, a new user profile may have been created. Check by browsing to My Computer > C: > Users (or Documents and Settings). Then look at all the folder names. Take a look inside any that look promising.
If files were indeed wiped out, you could try a file recovery program. I use GetDataBack for NTFS
but that is not free. Your mileage may vary with the free ones. GetDataBack is very good in my opinion, but even that won't recover everything, especially if the files have been physically overwritten.