I will assume that you do not plan on having it taken to a shop
After four months-- have you done anything in the way of testing
or even have those skills with vehicles
A failed & almost dead battery, will still turn on the radio & lights,etc
That is not a test for anything
Your Battery has to have 12.6 Volts before you start any testing
By turn over, you mean the motor turning,moving or cranking,your
preferred terms ?
You have a No Crank or a No Start-pick on !
The battery cables have to be removed & cleaned on both ends, of both cables,
as well as the starter terminals
You could have the starter tested at the parts store, if testing on vehicle,
is not your thing
You could swap out the starter relay for a similar one near it
You could move the gear shift to close the neutral safety switch
Check ALL Vehicle fuses
Nothing got wet did it ---under hood fuse & relay boxes ?