i have a question about the new d&d 4th edition?

Assuming you have all your powers available at the beginning of an encounter, you can use any or all of your encounter powers during that encounter. Once used, a given power cannot be used again until you have had the chance to take at least a short rest (barring an item like a Power Jewel or some other power which permits you to recharge one.) Similarly, all of your daily powers are also available, but they only recharge after an extended rest.

The only other limitation on number of resources usable in a given encounter that I recall is that for Action Points and item daily powers - generally, you are limited to using 1 AP per encounter (regardless of how many APs you have saved up) and 1 item daily (regardless of how many items with daily powers you posess). Certain feats or paragon paths may change this, at least as far as APs are concerned.