Re: ceiling fan ?
First, why did the fan fall and have you rectified that problem before trying to install a new one?
You should have at least a black and a white wire at the box. The wire housing can yellow over time, but there should still be a discernible difference between the two wire colors. If you've got older knob and tube wiring, hire an electrician to make up the connections for you, they've got the right diagnostic equipment and expertise to install the fan correctly.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!