Your welcome - If the grout is loose you will want to scrape anything loose, re-grout those areas, and then re-seal. If you cant match the color of the old grout you may need to re-grout the entire thing. I haven't had much luck grouting over old grout, it should be removed. There are special scrapers made for removing old grout. You might find them at the home center and definitely you will find them at a specialty tile store.