differential equations - collecting terms with different order

I am using homotopy perturbation method to solve nonlinear ODE.

The first step is to introduce P parameter and collect different order of P.

The code is like this:

Collect[(1 - 
 p) ((((1 + 
       De^2 (Derivative[1][u0] + p Derivative[1][u1] + 
          p^2 Derivative[1][u2] + p^3 Derivative[1][u3])^2)^(
     1/2 (-3 + n)) (1 + 
       De^2 n (Derivative[1][u0] + p Derivative[1][u1] + 
          p^2 Derivative[1][u2] + 
          p^3 Derivative[1][u3])^2) (Derivative[2][u0] + 
       p Derivative[2][u1] + p^2 Derivative[2][u2] + 
       p^3 Derivative[2][u3])) (Derivative[1][u0] + 

     p Derivative[1][u1] + p^2 Derivative[1][u2] + 
     p^3 Derivative[1][u3])) + (1 + 
    De^2 ((Derivative[1][u0] + p Derivative[1][u1] + 
        p^2 Derivative[1][u2] + p^3 Derivative[1][u3]))^2)^((
   n - 1)/2) (Derivative[1][u0] + p Derivative[1][u1] + 
    p^2 Derivative[1][u2] + 
    p^3 Derivative[1][u3]) (Derivative[2][u0] + 
    p Derivative[2][u1] + p^2 Derivative[2][u2] + 
    p^3 Derivative[2][u3])) + 
  p (-Ha^2 (u0 + p u1 + p^2 u2 + 

    p^3 u3) + (((1 + 
       De^2 (Derivative[1][u0] + p Derivative[1][u1] + 
          p^2 Derivative[1][u2] + p^3 Derivative[1][u3])^2)^(
     1/2 (-3 + n)) (1 + 

       De^2 n (Derivative[1][u0] + p Derivative[1][u1] + 
          p^2 Derivative[1][u2] + 
          p^3 Derivative[1][u3])^2) (Derivative[2][u0] + 
       p Derivative[2][u1] + p^2 Derivative[2][u2] + 
       p^3 Derivative[2][u3])) (Derivative[1][u0] + 

     p Derivative[1][u1] + p^2 Derivative[1][u2] + 
     p^3 Derivative[1][u3])) + (1 + 
    De^2 ((Derivative[1][u0] + p Derivative[1][u1] + 
        p^2 Derivative[1][u2] + p^3 Derivative[1][u3]))^2)^((
   n - 1)/2) (Derivative[1][u0] + p Derivative[1][u1] + 
    p^2 Derivative[1][u2] + 
    p^3 Derivative[1][u3]) (Derivative[2][u0] + 
    p Derivative[2][u1] + p^2 Derivative[2][u2] + 
    p^3 Derivative[2][u3])), p]

The problem is that don't get anything back

What do you think?