Are you burying the entire seedling? I always just lay the seed on top of my soil and spray it down good and put it in my grow room for the heat in the 19 inch tray so I can do at least 12 at a time. I found that covering the cups with large cardboard keeps it dark yet warm due to 400w hps. The seed pops in 2-4 days and then I take a tooth pick and poke a hole and guide the tap root in the hole and make sure the seed is above ground and only has to push the shell off. after the seedling grows about an inch and a half I fill the cup with more soil up to the leaves and move it under the lights to keep my stems nice and thick. I forgot to mention when I fill the solo cup with soil I leave about an inch or a bit more below cup level so after the seedling pops and grows its skinny ass about an inch I bury that inch up to its neck and then Its on Baby. If you do this and its warm and it dont pop then your seeds suck or you may have a strain with this trait. Good luck man warm the seedlings more if you havnt already and get the seed above ground and dont bury it anymore. Just the way I do it others can offer other ideas but this is my seed pop recipe. I have never had to wait more than 5 days for a seed to pop with the strains I have been growing. take a peek and make sure its not growing sideways if you buried it. Good luck man