DIAGNOSIS The LED itself rarely fails. The issue is almost always a broken wire or a poor connection where the light's wiring meets the main circuit board or trigger, or the LED board came loose from vibration.
FIX You'll need to open the saw. Remove the battery and the four long body screws. Once open, locate the small circuit board for the LED—it's right behind the clear plastic lens in the front. First, check the two tiny wires running from it back into the body. Vibration often breaks one right at the solder point. If you see a broken wire, you can carefully resolder it. Also, check that the LED board is still snug in its slot; sometimes it vibrates out.
IF THAT DIDN'T WORK If the wiring looks intact, the LED might have gotten zapped by a power surge (rare, but possible). You can test it with a multimeter set to diode test, but replacing the little LED board is the practical fix if you've confirmed power is getting to it.
HEADS UP When you reassemble the saw, be very careful routing those tiny LED wires. Make sure they aren't pinched between the housing halves when you close it up, or you'll just break them again.