Question: how can I solve an equation?

Hi all
how can I solve an equation? Pleas, help!

I have a differential equation with one unknown.
I first solve the differential equation, and then use the boundary condition to find his unknown, however, get the error:
Error, (in sol_2) parameter 'X' must be assigned a numeric value before obtaining a solution.

How can I find X?


 eq := diff(V(z), `$`(z, 2)) = B*(abs(M_x(z))/J_nc)^n*signum:cond := V(0) = 0, (D(V))(0) = 0;
 sol_2 := dsolve({cond, eq}, numeric);


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