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Hi, the first thing you should do is connect a jumper battery to the car again and see if it will start. If your battery is a little weak it will cause the starter to crank briefly and then stop.
I think you might just need to replace the battery but another possibility is excessive corrosion build up on the flywheel. The corrosion can cause high resistance in the starter and cause the start cycle to end prematurely. It was common to have to remove the starter and lubricate the flywheel with a little bit of anti seize paste.
You can also try turning and holding the key in the start position rather than releasing it and see if it will crank.
Let me know how you make out.