Well first thing is that not all
seeds will sprout at the same time, although 2 weeks seems long enough to wait. You can read the package to see what it says about germination time. I also had the same problem with spinach seeds myself, I went through a whole package of seeds and only one seed ever sprouted but never grew. It's quite possible that you have gotten a bad batch of seeds, or perhaps they were just to old sitting on a shelf before someone bought them. The package should have a sell by date on it. Most seeds should sprout at about 85 degrees as far as I know, so if that is what the temp is inside the little greenhouse that should be fine. if it's cooler it may just take longer, and if it's real cool I'm not really sure. But if it's much over 90 you will probably just be cooking them. From my experiences seeds are very sensitive to temperature.
P.S. the rockwool cubes should be just moist or slightly damp, not soaked. If it is too wet there wont be enough air in the media and the delicate tiny hair like roots can suffocate. The plastic lid will keep them from drying out by keeping the humidity in. You can always give them a quick spray from a spray bottle if it seems like they need it, but the lid should keep them moist.