In Steve's original post he said that he sowed grass seed (in March) and then covered the seed with 2cm of top soil. Alina gave this diagnosis for the seed not coming through:
There may have been too much soil covering the grass - it is normally sown virtually on the surface.
If the seed was buried, then it doesn't have much chance, and will rot, I'd have throught.
Grass seeds are not like things like sweet peas which do need a deep covering. Most small seeds can be sown on the surface, or very lightly covered. But not 2cm. When sowing grass, a gentle raking should be enough, so that the seeds just sit among the bits of soil.
Sprinkle some more seed on top, over a small test area, asap, and see what happens.