Car doesn't start

Did you pre-charge the new battery? Look for badly corroded battery cables that may be limiting the voltage to the starter. If you have access to a voltmeter, check between car ground and the positive battery cable connection on the starter solenoid. You should read 12.6 volts DC. Try to start the engine--if the voltage drops very low, the cable is likely bad. Check between the negative battery terminal and the engine block--try to start the engine--you should not see any voltage at any time. If it jumps to 12.6 volts, one of the negative cables is bad (either the one from the battery to the body or the one from the body to the engine block). There is smaller possibility that the starter motor is jammed and will not turn causing a very heavy current draw. It would need to be removed and tested at an auto parts supply. Hope this gets you running!

Tap on starter and same time get sambody to start if start replace starter

There are a few things to check that are pretty easy. First there is a fuse (30 amp fusible link) located near the battery labeled FL30 IGN SW. If possible check it with an ohm meter or continuity tester. Next on the passenger side, under the hood check the inhibit relay. With the key in the on (not start) position remove/insert the relay. You will be able to feel it energize. This does not prove that the relay is good only that it should be working. If it does not energize, the problem may be your ignition switch or the relay may be bad. With the relay out check the relay socket with your voltmeter for 12 volts accross the coil (shown on top of the relay) if the voltage is there and the relay did not energize it's bad, replace it.

Now it's time to get dirty. Read the following text then get under the car with your volt meter. Check the voltage at the starter solenoid (move the black rubber boot out of the way) with the key on or off (does not matter) you should see 12 volts DC (12.3-13) use the chasis for ground.(a steel bolt through the frame or engine is good) If the voltage is good take a screw driver, hold it by the insulated handle only, and make contact accross the 2 large terminals on the starter solenoid. This will cause some arching at the terminals and is normal. This will bypass the solenoid and a good starter will crank at this time. If it does not then follow the directions and take the starter out, carry it to the auto parts store and they will test it for you. If it does crank here but not from the key you have a soleniod, inhibitor relay or ignition problem.

I could not find any guide for removing the starter from a 1.6L 1999 Nissan Sentra, Incl. Haynes and Chiltons. Remove the air box top, filter, MAF and duct. Remove the three screw/bolts from the bottom of the air box, and set the box aside. Disconnect the battery terminals and follow the negative cable to the bolt thru the bellhousing and into the starter. You just found the starter. Remove the bolt from the starter but leave it in the hole through the bell housing. Just to the right is an electrical connector, disconnect it from this side. It is the control line to the starter soleniod, which is mounted to the starter. Lift the car and put jack stands under the front on both sides (Remember to set the parking brake and chock the wheels). Remove the passenger side front tire and plastic shield allowing you to see along the back of the engine to the tranny. Loosen the support bar from the intake manifold to the frame below/behind the oil filter. You will now be able to get a socket with extension to the starter bolt. You can now see the starter and solenoid. Remove the positive battery cable from the solenoid stud. Remove the remaining bolt holding the starter in place. By wiggling the starter it can be removed without removing the oil filter, although that might make it easier.
You can not remove this starter from above, you must raise the car and work from below. I removed the battery from the car while working under the hood, it only took about a minute and gave me alot more space.
I did check the starter before disconnecting the battery by shorting accross the starter solenoid. If the starter had turned over the engine I would not have continued to remove it.