Very often magento 1.7 search is not working as we want. It returns non relevant search results. Part of the problem can be solved by the correct settings. Go to System -> Configuration-> Catalog. Open tab Catalog Search. Try changing the settings of "Search Type" and see what happens. Sometimes it can temporarily solve the problem.
If in this way the problem persists, then it's optimally to install Magento search extensions, which improves search quality by using a search engine Sphinx or Solr. One of good examples of such extensions is Advanced Sphinx Search Pro.