DIAGNOSIS A complete lack of response, even with a known-good battery, points to a break in the electrical circuit. The most common culprits are a faulty trigger switch or a loose internal connection.
FIX Start with the simplest things. 1) Ensure the chain brake is disengaged (handguard pulled back). If it's on, the switch is mechanically blocked. 2) Try a different 20V Max battery, even if you think the first one is good. 3) Inspect the battery terminals on the saw and the battery for dirt, debris, or bent contacts. Clean them with a dry cloth. 4) Look for any obvious damage to the trigger or wiring you can see without taking it apart.
IF THAT DIDN'T WORK The issue is likely internal. There's a small circuit board and switch assembly. If you're comfortable, you can remove the housing screws (remembering their positions) to check for disconnected wire plugs or burnt components. Often, the trigger switch itself fails. For most people, this is the point where a repair at a DeWalt service center becomes the most reliable option.
HEADS UP Before you do any disassembly, remove the battery. There's no lingering charge, but it's just good practice. Also, if your saw is still under warranty, opening it up yourself might void that coverage. If simple battery/brake checks don't solve it, a professional diagnosis is the next smart step.