re read this last night
1. Old ones created vast empire
2. Necrontyr were younger race, because of their fraility due to their sun they resented and tried to fight old ones, pretty much lost and were almost wiped out, despite their superior technology, they could not cope with old ones manipulation of the empeium (warp)
3. Necrontyr descover C'Tan living off solar radiation, they have existied for ever (i.e. predate the old ones) but (interpretation) are more like animals than a higher race. Thje necrontyr gave them phisical form made from living metal (whatsidermis) at which point their sentinence became apparent, as did their hunger, in return they they became gods of the necrontyre and offered imortality to the necrontyre, giving them metalic bodies and in turn consuming the organic bodies of the necrontyre, hence necrons were born from the necrontyre race which died. (note as I see it this means there is only a finite number of necrons)
4. the necrons and C,Tan now started to attack the old ones, and start to win, desperately the old ones started to create (the) younger races with more and more psychic ability, notably the eldar originated during this period, despite this the C'Tan and Necrons continue to win, subjugating most of the galaxy and harvesting them, the C'Tan start to fight amongst themselves, and the old ones finally create the enslavers, who becoem totally out of control
5. the C'Tan and necrons faced withthe enslavers decided to withdraw from an active role in the galaxy and wait until all the psychic activity created by the old ones dies down, they go to sleep, onyl to wake up when a race whose signature is suitable for them to harvest intrudes on their tombs
6. The old ones have withdrawn/left, the rise of the eldar empire
7.The fall of the eldar, in the absence of the old ones, some of their most recent creations go awaray, (humanity)
8. humanity starts to wake the Necrons/C'Tan, although there is still far too much of the Empyrian about