Step Response Parallel RLC
If you truly have no idea at all where to start, then you are trying to get into the wrong field.  Surely you know something.  If not, bail out now.

We can help when you get stuck on something specific, but aren't going to do your homework for you.

Hint: You can combine the voltage and the current source into a single equivalent source.  Look up Thevenin and Norton sources.  You can go further and combine that with R3.  I would simplify the whole thing to a Thevenin source driving a parallel LC, with the appropriate initial conditions.