Most likely reason (90% of the time) is due to a low charge on the battery, most garages will be able to check the battery charge (normally or free), otherwise your earth cable may not have a great connection, or you have a worn starter motor.
The problem is in the starter drive (sometimes called bendix). Take the starter back to wherever it was rebuilt and have it repaired or exchanged.
starter is out, motor is locked up or your starter solenoid is out.
It will probably be your starter motor Starter is out!
It will not turn over on the starter motor.
the starter is bad.
Could be the starter relay
When the starter motor refuses to turn over or grinds and clicks when turning then you need a new motor or recondition the old one.
A starter motor turns the engine initially whilst fuel is vapourised in the rotating cylinders and ignited, taking over from the starter motor.
A bendix.
if the motor is spinng over then starter is ok
if engine will not turn over, check fuses first. then check battery, starter motor, starter motor solenoid and ignition switch
A small electric motor used to turn an internal combustion over to get the larger engine running.