Spotlight doesn't find everything?
Apart from it taking some time to display everything it finds (so you might have to, well, just wait a little longer, it could be that you're trying to find something that's on a FAT32 formatted (Windows) external drive. Those are not fully indexed by content/metadata, i.e. Spotlight will only find your search-terms in the filenames for those drives. There is not currently a solution to this (i.e. you won't be able to metadata-spotlight such a device). A workaround is to reformat the drive (make sure to back it up!) in Mac OS Extended (HFS+) format. But then you can't share the drive with PC users any longer.