To solve the inequality \(x^{3}(-3x-8)^{4} \leq 0\), we first find the critical points where the expression equals zero. The expression is zero at:
\[
x = 0 \quad \text{and} \quad x = -\frac{8}{3}
\]
Step 2: Analyze the Sign of the Expression
Next, we analyze the sign of the expression \(x^{3}(-3x-8)^{4}\). The term \((-3x-8)^{4}\) is always non-negative since it is raised to an even power. Therefore, the sign of the entire expression depends solely on \(x^{3}\). The expression \(x^{3} \leq 0\) holds true when:
\[
x \leq 0
\]
Step 3: Determine the Solution Set
Combining the critical points and the sign analysis, we find that the inequality \(x^{3}(-3x-8)^{4} \leq 0\) is satisfied for:
\[
-\infty < x \leq 0
\]
Final Answer
The solution to the inequality is:
\[
\boxed{(-\infty, 0]}
\]