Water not reaching the overhead tank from mains pipe- flow ground to top to the overhead tank
Water pressure at the ground level is the issue here as your pipes go up you lose pressure at .445 pounds per foot 5 stories up ~50’ your pressure would be ~22 psi less this may not be enough pressure to open the valve to the tank. If you are on a well you can increase the cut out pressure on your pump. If on a city water system contact them about the low pressure. Other than that a booster pump to increase pressure may be needed to provide enough pressure for the tank to fill.