have you thought about testing your soil? the local county extension offices administer soil tests for a small fee (mine here in nj charged me $15). if manure, peat moss and fertilizer do not work, it sounds like something might be really wrong with your soil. only a soil test will tell you. once you get the results, you can go look on the soil forum here on gardenweb to find out how to fix whatever the problem is. hope this helps.

i had heavy clay soil here in nj, and got a soil test done. nothing was too bad, it just needed a lot of compost mixed in to lighten the soil. all my vegetables are doing very well. it sounds like you are doing the same thing and your plants are dying, so it's probably somethign else that's causing it.