Impatiens not growing

I'm confused and can't find any answer on the web. My impatiens germinated in about 10 days in soilless medium, but it's 5 weeks later and they still look the same as after 10 days. They haven't even put out their first true leaves. What would cause them to just stop growing right after germinating?

I am having the same trouble right now with some of my seedlings! They all germinated just fine, and then- no true leaves... they're just stuck. (Not impatiens- just basil and tarragon). So, I've been trying to look into what the trouble is. So far what I've found is that some kind of shock, like a drastic temperature change, can do that, or that it can also happen with old seeds. Mine WERE from seeds I didn't use up last year and had kept in a baggie in the fridge, so I'm guessing that's the trouble. Since they aren't anything expensive, I'm thinking of just moving them out into the garden and seeing if anything happens - though I'm guessing they might just burn up in the sun. I'll be curious to know what happens with yours.

I had the same problem but it turned out to be a fungus gnat problem. The larvae were feasting on the roots . . .