The Makita 18v cordless drill is a usually reliable power tool, but with heavy use even the most reliable tool can have problems. In a cordless tool the most common problem is a dead battery or a faulty charger, which are relatively easy to detect and fix. If the problem is in the actual drill, detection is a simply matter of testing its various functions methodically. Makita stands by its products and will usually repair faulty units without much hassle.
Plug the charger into the wall socket. If the charger is functional, the lights will flash once. Then the charger will display a green light next to "ready to charge." The temperature gauge should flash green, indicating that the charger is not overheating. If the gauge flashes red or yellow, then try moving it to a cooler place. If it still flashes red or yellow, then the unit has a faulty cooling fan and needs to be replaced.
Plug in the 18-volt battery into the Makita recharger. The recharge light on the charger will be a steady yellow while it is successfully charging, turning to green once it is fully recharged. You should also hear a faintly audible hum of the power inverter; this is normal for an 18-volt recharger. If the recharge light flashes yellow or red, then the battery is broken and must be replaced. There is no fixing a lithium-ion battery; you can only replace them. Take the dead battery to a proper recycling facility.
Insert the battery into the drill. Pull the trigger and see if the chuck (the thing on the front of the drill that holds the bit) rotates. If yes, then the drill works. If not, then select the reverse gear and see if the chuck rotates. If the chuck only rotates in one direction, then a gear has broken--either its teeth have worn down or it is no longer meshed with the opposing gears. You will need to take it to a service center to be repaired.