Depending on the temp in your ziplog bags, also if the sunlight comes (through the window) over the bags, if the temp was too high you cooked the seeds.
If not, maybe too low.
I used too this method (slightly different, not in a bag, but in a box, covered) and maybe I am not skilled enough or what, but I think will use no more. I have the feeling the plants grown this way are not so health (or at least as seedlings). I am using something from supermarket, some cells, where I put the soil, not filling them completely, watering, put the seeds, put a transparent cover. When the seeds start to sprout, I cover them with a tiny layer of soil. This way I can see if they are sprouting, and they grow directly in that soil.
Put some picture, maybe will give a hint to somebody (a picture worth more than 1000 words).