\[ y''(x)=-\frac {y(x)}{(a x+b)^4} \] ✓ Mathematica : cpu = 0.150835 (sec), leaf count = 54
\[\left \{\left \{y(x)\to c_1 e^{\frac {i}{a (a x+b)}} (a x+b)+c_2 e^{-\frac {i}{a (a x+b)}} (a x+b)\right \}\right \}\] ✓ Maple : cpu = 0.069 (sec), leaf count = 39
\[ \left \{ y \left ( x \right ) = \left ( ax+b \right ) \left ( {\it \_C2}\,\cos \left ( {\frac {1}{a \left ( ax+b \right ) }} \right ) +{\it \_C1}\,\sin \left ( {\frac {1}{a \left ( ax+b \right ) }} \right ) \right ) \right \} \]