Power went out, we were running multiple window AC's the night it happened. I came up, plugged in my desktop computer to the outlet (it was unplugged), and powered on the PSU when it went out. There are 5 rooms upstairs, ones out are my room, master bedroom (incl bathroom), and the middle bathroom.

Strangely though, ALL the ceiling fans have lost power, even the ones in the rooms with power still.

My father tested using a voltage tester and can't seem to find the issue. We replaced all the outlets he re-grounded them. We opened some of the ceiling fans up and checked those wires as well but can't find anything wrong at those ends.

Any help?

There must be a loose or open connection somewhere in the circuit. Ned to begin at the panel, checking for power at the breaker, and then follow the circuit wiring to each outlet, junction box, etc, checking for power and looking for that defective connection.

There is no shortcut for this problem, other than systematically checking each splice or connection point in the circuit.