If there is nothing to see at all, it is usually to do with the fact that the seed is refusing to germinate (for whatever reason). This is why I prefer the method of soaking the seed well, then placing it on a piece of kitchen roll and placing it in the germination tray. Only when I have evidence of the emergence of 'life' will I place it in the soil.
My motto is always - the proof of the pudding is in the eating!