Sometime the crawl in Windows SharePoint Services gets stuck, doesn’t run or simply misses sites because of other issues (security, configuration, etc.). In MOSS and Search Express, it’s easy to kickoff full crawls when these kinds of problems happen. You would need to initiate a full crawl, because nothing new would be crawled during the outage and when you have resolved your search problems, you would be missing that data in your results.
Thankfully, this one is quite easy. Utilizing the STSADM command out of the hive, you can start and stop full crawls. In some cases, I've even added this as a scheduled windows task to make sure that WSS runs a weekly full crawl.
To start a full crawl of the content, use the following syntax:
Stsadm -o spsearch -action fullcrawlstart
To stop a full crawl of the content, use the following syntax:
Stsadm -o spsearch -action fullcrawlstop