I cant read that dark, blurry drawing so i'll just offer a hint going by what it looks like you are after.
First, i assume that the switch was on for a long time relative to the longest time constant of the circuit, then at t=0 it is turned off (opened), and you want a solution such as the voltage across the capacitor which is the voltage across the lower RLC network.
If that is the case, then the only element that has energy in it at t=0 is the inductor so you can handle this circuit as a parallel RLC circuit with only initial energy in the inductor. So the inductor current at t=0 is the only thing that drives the solution (no other driving force at that point in time).