New battery but will not start up sometimes

No click no sound at all.

I would start by checking the battery. It could be just at the borderline where there is not enough charge to activate the starter motor. If the battery tests good, then it's time to start checking all cabling connections - ensure all battery cables are secure and free of corrosion. If this is an automatic transmission vehicle, the ignition system will need to see the vehicle in "park" or "neutral" gear to start the vehicle. It is possible that for some reason this is not the case -- ensure the shift lever is in park or neutral. A diagnostic tool is helpful to determine what the sensor for the transmission gear selector is seeing as far as selected gear. Those are a few areas to go on, but the best thing to do is seek guidance locally at a shop near you that can help.