Seedling Help!

[SpaceCadet]

I started some tomato, cilantro, jalapeno, cucumber, and nasturtium seeds in pots for my container garden. The cucumbers have gone totally crazy and the jalapeno are doing well, but my nasturtium and a couple of the cilantro and tomatoes have suddenly taken a turn for the worse. They each have a leaf or two that have just suddenly shriveled and dried up, and I can't figure out why. =/

Here's how they're being housed at the moment: each of them are currently planted in a plastic cup (the ones you get in 24-packs at the grocery store) in the organic Miracle-Gro potting mix with a little bit of the seed-starting mix on the top. (They were transferred into these cups following my realization that they were growing out of their little greenhouse thingy much more rapidly than I had anticipated.) I attempted to replicate the greenhouse atmosphere by taping clear plastic cups over them to keep the humidity up. The soil in each cup was wet thoroughly when I planted the seedlings, but hadn't been watered since. I did check the soil every day, and it was always nice and moist. I watered them after noticing the wilting leaves, thinking that maybe for some reason the top of the soil was wet when the middle/bottom wasn't? Oh, and I punched holes in the bottom of the cups for drainage, so I don't think overly-wet soil is the problem. They're all lined up on my office windowsill, which faces north so they never get direct sun. I do, however, keep a 150-watt grow lamp nearby and it's on for most of the day. It's about 2-3 feet away from the seedlings (pointed at the cukes, since they're the ones going bananas in their pots). I moved the suffering plants closer to the light source, thinking that lack of light might be why they're doing poorly, but it's been too soon to be able to notice any kind of change.

I always plant more seeds than I need to, to plan for contingencies like this, but I think it would be swell to not lose baby plants this year. I think the nasturtium is beyond saving at this point, as both of its leaves are just crunchy shriveled little stubs, but the cilantro and tomatoes can still be salvaged, I think, if I can figure out what's wrong.

I Googled "shriveled plant leaves," and Google suggested that perhaps I had watered them too much, or too little, or that they were getting too much sun, or not enough sun, or maybe that they were rootbound, or that there was too much fertilizer used. I've attempted to remedy the watering/sun if either of those are indeed the problem, and I don't think the others apply, but Google also said it might be a plant disease or a fungus. The seedlings have all been indoors for the duration of their short lives, and the wilting seemed to happen overnight (literally - last night when I put them to bed, everything appeared fine, and this morning was when I noticed the wilting). I don't know where they would have gotten a plant disease, and I don't want to treat for something they don't have (especially since they're so small and I'm afraid some kind of fungicide would kill them along with the fungus or whatever it is).

This is my first year gardening somewhere where there isn't a lot of humidity (I lived in Florida, and now I'm in Utah), so I've been changing my tried-and-true methods for gardening in order to compensate for the 0% humidity (ok maybe not 0% but man does it feel that way sometimes). Any help would be appreciated for my poor little seedlings!

[rainbowgardener]

I have to say, I have grown nasturtium from seed other years and it did great. This year not much of it germinated and the ones that did just shriveled up and died. Not damping off, they withered up.

Everything else did great! Sometimes it just happens!