Car will not start. Checked battery. ok. Tapped the starter motor with hammer. Vehicle started. Let sit over night. Same condition. Will not start. Vehicle is a Pontiac Grand Prix 2006, 3.8 Supercharged, 110,00o miles. Second Owner.

The first thing you do is have the condition of the battery checked because if the battery is weak the starter motor will not operate.

See if you can jump start the car from another vehicle. If you can you know the battery is the problem and you need to replace it.

Joe, was a bad battery causing the start problem? or did you assume it was the battery?
Not knowing what is wrong, can cause you to replace lots of things, without resolving the real problem.
The could be a bad starter relay, a bad cable or just a bad connection to the starter motor. But also dead point in the starter motor. First try to do a correct diagnose, by testing things and then replace. Making a diagnose, not being close to the car is almost impossible.

Okay it says you checked starter motor and it tested good. what test did you perform? A bench test would tell you if solenoid is good or bad. Try this With starter in vehicle and key on, jump positive power to solenoid it should spin and engage flywheel and start vehicle

perform bench test with starter in vehicle

Sounds like a weak battery
Try with another known good battery

Also check/clean battery and Starter connections and earths

starter motor most likely to be at fault or at least the starter solenoid

The clock resets because the car battery voltage/current is so low that when the starter motor is turned the + 12 drops to less than 8 volts and so the CLOCK resets.
Please have the battery checked, check the starter motor , battery terminals must be tight.

Try having one person turn the key to the start position and hold it there, while someone else taps on the starter with a hammer. If tapping on it makes it work, you need a starter. Good luck. Hope this helps.

it could be a lose belt or try to recharge the battery

Starter motor or solenoid is going bad or cables are corroded. Clean all cables if car does not crank have someone try to crank it while you "smack" the started motor housing with a hammer or a long solid rod (hitting the rod with the hammer as it rests on starter motor case). Hit it sharply a few times. If it starts, then the starter motor is bad.