I am not sure if this helps, since your question is vague and open-ended. Anyway, after you do your analysis through the GSEA tool, an 'index.html' file is generated with the enriched gene sets for positive and negative phenotypes, along with detailed enrichment results. If you have no enriched gene sets in the negative phenotype, you might have to go back and check the following:

1. If you run Pre-Ranked, then try ranking the genes through a different metric (p-value is not a good ranking metric).
2. Try using different gene sets, narrow or expand them.