My knee hurts when straighten and when I close it. Would an ACE bandage do any good?

Swelling? If the knee is swollen, then both the straightening and bending of the knee beyond 30 degrees causes pain that is due to increased pressures in the knee and stretching of the capsule of the joint. If you have had a recent injury that has left your knee swollen and painful as you described it, it may be due to soft tissue injury sustained by your ligaments or menisci. Need to be evaluated!
Ace bandage. This may give you a little support but won't treat the problem. Keep weight down, exercize, see your physician if symptoms continue you may need pt.