  In this paper, we consider the following eigenvalue problem {{l}
(|u"|^{p-2}u")"=\lambda m(x)|u|^{p-2}u, x\in (0,1), u(0)=u(1)=u"(0)=u"(1)=0,
where $1<p<+\infty$, $\lambda$ is a real parameter and $m$ is sign-changing
weight. We prove there exists a unique sequence of eigenvalues for above
problem. Each eigenvalue is simple and continuous with respect to $p$, the
$k$-th eigenfunction, corresponding to the $k$-th positive or negative
eigenvalue, has exactly $k-1$ generalized simple zeros in $(0,1)$.
