Engine won't turn over and starter motor makes a thud sound

Brand new starter motor and brand new ground cable to battery. Battery is 100%. Changed spark plugs, changed coil packs, changed boots, brand new fuel pump, and brand new valve cover and gasket. After I replaced everything, it turned over briefly, twice when I tried it and now it just does the thud sound from the starter when I turn the key in the ignition every time. Any help would be greatly appreciated, thanks.