Probably Version issue. Maybe this helps:
Assuming[{Re[\[Beta]] < -1/2, Re[\[Alpha] + \[Beta]] > -1, Re[y] > 0}, Integrate[BesselJ[\[Alpha], x*y]*x^\[Beta], {x, 0, Infinity}]]
(* Or: *)
Integrate[BesselJ[\[Alpha], x*y]*x^\[Beta], {x, 0, Infinity}, Assumptions -> {Re[\[Beta]] < -1/2, Re[\[Alpha] + \[Beta]] > -1, Re[y] > 0}]