Hi,
This page is used to setup category searches.
http://www.auctiva.com/stores/editstoresearch.aspx
My guess is your "Match Logic" is probably too restrictive on link settings, i.e. ALL WORDS present as a requirement might yield no results. Checking your Category links seems to verify that problem, e.g. the Violin Strings link will only match with "Dominant Perlon Violin Strings" (all words). However, if I force a search to just "Violin Strings", I get two hits.
http://www.auctiva.com/stores/...in%20Strings&logic=0
Danno