incubating egg problem!

advice please, don't know what we are doing wrong. Have bought a new digital incubator, and put in a mix of 18 eggs, bought from ebay, have done every thing by the instruction book, changed temperature and humidity on Tues evening, and nothing yet has happened, have just tried to candle them for the first time, but all I seem to be seeing is air sacks.

How many days have they been in the incubator now?

Just to add, what sort of incy do you have? what did you have humidity and temp at and what did you change it too?
finally (sorry for all the questions! )...when you candled the eggs, did they look mostly dark with a clear air cell roughly just under a third of the total egg volume? if you did then they are viable, if they are clear ie. the same as an unincubated eggs then they are infertile.

Hi Bobbie, well going on my reckoning hatch day was Thursday so they are on day 23. The humidity sounds maybe a little high, with chicken eggs I run between 30 to 40% humidity and I dont raise humidity until there is external pipping, indeed many experienced chicken keepers run the incky dry until pipping, as the ambient humidity is enough in the UK this time of year.  Temp at 100.5 is 38degrees should ideally be 37.5.Leave them for a couple of days yet, you might be pleasantly surprised! It is difficult though, sometimes eggs dont travel well through the post so if they were damaged then the best incky in the world isn't going to help really.
BTW did you see a small or large air sac on candling??

I have just checked the eggs, and I think some have a dark area which could be described as like a yolk, some are completly clear and one aleast is very mottled, which I don't think is a good sign, have switched the humidity off, should I turn the temperature down a bit, and leave them a few more days.
Have you any advice on where the best place to get some firtile eggs from,

We live in Crawley, West Sussex. Already have 16 girls, 10 warrens, 2 columbian black tails, 2 light sussex, 1 moran and 1 bovan, looking for something different, not bantams,
Not into ducks yet, as just getting ready for when we evetually hatch a few eggs of our own.