I have an older chandelier with 2 unlabeled wire (a single double wire which has been split in two.) The junction box has a black, white, and red wire in addition to a copper wire. I attached the copper wire to the green screw, but I was not the one who removed the previous chandelier and do not know how to connect up the other wires. The house is new to me and there is both a regular and dimmer switch on the wall. I don't know if one or both are related to the light.

That red can mean a second switch some where also controlling power to the ceiling box. Put a tester between black and white and then try the switches, likely the regular switch. Now do the same between red and white, test both switches. I will take a wild guess the dimmer may be controlling the red iwre but tell us what you founs and we'll figure a fix for your issue.