Well, nems will "shrivel" up from time to time, usually about once a week and for a period of anywhere from a few hours to a little over a day. They expel the liquid/orgamisms within them just like a lot of corals do. If it has been closed since you got it, then it may be injured. Just be sure to watch for disintegration. If it has just recently began to look this way, I would not be too concerned. It may also be adjusting to the new lighting of your tank. What sort of lighting do you have? Also pics would be very helpful.
As far as feeding, making sure you're feeding it finely chopped marine foods, i.e. mysis shrimp, prawn, squid, silversides, whatever, as long as its smaller than the nems mouth. It will usually only accept food when it is "inflated" so trying to feed it otherwise may stress it out. You need to mix the chopped food with a bit of tank water, then spot feed the nem with a dropper or syringe, spraying the food NEAR his mouth but NEVER in his mouth. I used to just spray my condys tentacles and let him do the rest of the work.