Battery
If the drill isn't getting power, it is most likely the battery. The average nickel-cadmium battery lasts only a few years. If the battery has been overused, it will die even sooner. Buy a new battery.
Battery Charger
The battery can be wrongfully accused of being the culprit for the drill problem if the battery charger is faulty. If the charger isn't working, the battery will never get charged. Place a battery into the charger. If no lights come on, the charger is not reacting to the battery placement.
Drill Chuck
A lot of pressure on the bit area can cause the drill chuck to cease up. If a bit will not lock into the chuck or will not spin, it is a chuck problem. The chuck can be replaced by popping it off the drill with a flat screwdriver.
Trigger
The trigger can lock up, causing the drill to not work at all. It can be frustrating, since there is nothing wrong electronically with the drill. Replacing the trigger requires taking the drill casing off with a Phillips screwdriver. The trigger is locked inside the drill with a screw. Once it is unscrewed, the trigger can be replaced with ease.
Drill Motor
If every avenue has been tried, the drill motor will need to be replaced. The motor is above the handle behind the chuck. After removing a few screws in the casing, the motor will pop out.