5 Year Old--Won't eat!!!?

My 5 year old stepson refuses to try anything new to eat. We have to fix two separate meals at every meal. He will only eat the following: pb&j, chicken nuggets and fries (no tenders, has to be nuggets), hot dog, pancakes, cheese and crackers, breadsticks, chips and salsa. We have tried everything, punishment, rewards, begging, we even said he couldn't have anything but water till he tried something, and he just wouldn't eat for 3 days!!! We are at wits end. We've talked to a nutritionist, and her suggestions didn't work either. Any ideas? Please help!!!!