Why won't my car turn over

"I tried to start it back up and got one hard click and nothing.. brand new battery!" Well, eliminating the battery from a loud click, no starter sound, may be pointing to; battery cables, their connections, starter, alternator and drive belt system. Main power. Go over main power connections; both battery cables, their connections to battery (corrosion interfering with power), and grounds (battery to chassis, chassis to engine block). Battery voltage should be around 12.5vdc. If less than 12v, examine the drive belt for a worn/loose belt tensioner. With engine idling alternator output should be around 14.5vdc (supplying vehicle electrical needs while recharging the battery after every start.

An original starter is now 16yrs old and how many miles? Starters do not announce their demise from wear and tear. They tend to last almost forever but a hidden wear items; brushes wear out with no time limit on them. A diyer may disassemble a starter to determine wear (bearings, start relay, brushes, commutator). Bench tests are never good as one moment a starter tests fine and next, fail. The loud click is the starter relay snapping a set of electrical contacts, sending battery power to the starter motor. If you can eliminate everything before the starter and find noting, the starter is likely worn out. One old school trick may help; bang the starter body a few times with a rubber mallet. This may allow another start and if it does, replace it.