\[ y''(x)=-\frac {y(x)}{(a x+b)^4} \] ✓ Mathematica : cpu = 0.168937 (sec), leaf count = 76
\[\left \{\left \{y(x)\to \frac {1}{2} e^{-\frac {\sqrt {-\frac {1}{a^4}} a}{a x+b}} (a x+b) \left (2 c_1 e^{\frac {2 \sqrt {-\frac {1}{a^4}} a}{a x+b}}+\left (-\frac {1}{a^4}\right )^{3/2} a^6 c_2\right )\right \}\right \}\]
✓ Maple : cpu = 0.06 (sec), leaf count = 39
\[ \left \{ y \left ( x \right ) = \left ( ax+b \right ) \left ( {\it \_C2}\,\cos \left ( {\frac {1}{a \left ( ax+b \right ) }} \right ) +{\it \_C1}\,\sin \left ( {\frac {1}{a \left ( ax+b \right ) }} \right ) \right ) \right \} \]