Scotty is right about the necessity for a domancy with VFTs, it's possible that was a factor but I am a little more hesitant to call that the cause. VFTs can usually go a season without a dormancy and make it ok (I have tried). Granted, lack of dormancy + death cube/garden center conditions too long + fluctuating environmental conditions is probably enough stress to knock it over the edge.
Still, I feel like further examination should be considered here- especially since you said it was doing well until you "planted it in soil" (Incidently, transplanting is very stressful on VFTs- particularly during active growth. Do this when they go dormant if possible). It sounds like a bunch of things may have contributed. I have not looked at your other thread, but here are some questions which could shed some insight (I am not necessarily posting these questions with the intent that you answer them all here but if you feel inclined, the answer could possibly give us more insight on what may have happened):
1) What kind of water did you give it and how? How much (if you used the tray method, how far up the pot was the water for instance)?
2) You said you used one part sand and one part peat. Was the peat miracle grow brand or enriched with fertilizers? What kind of sand did you use (was it coarse, fine, was it silica/blasting sand or something else)? When you say "half peat half sand" did you measure this when the peat was dry or hydrated? (hydrated is better as you get a correct ratio)
3) You said you gave them more light? How much before and after and what was the source? Did you acclimate it to the new light over time or rapidly?
4) When you said it looked good before the transplant- what did it look like? Was it growing real vigorously or did it look like it was recovering from previous stress and getting better (IE lots of new growth but not a lot of green foliage yet).
5) What kind of pot did you put it in?
Hopefully we can get you set up for next time! In the mean time, I am not sure what reading you have done but you are in luck because the best information on the planet can be found for free!!
Have you checked out the ICPS (International Carnivorous Plant Society) website? In particular the growing guides?
John Brittnacher, the guy who maintains that website, knows his stuff- he's a good guy too.
Another really good source:
Scroll down to the section on Venus Flytraps. These pages are by no means dry reads. Barry is very enthusiastic about these plants and it shows. His pages are quite entertaining. Barry Rice is awesome! Consider getting his book too if you are a book person- the pictures alone make it worth it.
Hope this helps!
Scot will be asking you more questions when I get one VFT and do the fridge thing for sure now I believe I can do this and keep my VFT a live this time?Thanks for all the info.. this will be of great help...