Bathroom fan/light switch stopped working when I put on a new switch

Check the switch with a meter? Rated for the fan's consumption? Anything else on the same circuit (working/not)? Was old switch bad or problem elsewhere? Breaker/fuse? More info pix?

No, the old switch was fine, just old and discolored, so I switched it with a new one which didn't work, so I switched that switch with a different one in case that was the problem and still nothing, the wiring is two separate cords each with a white, black, and copper wire, the white and copper are connected with screw nuts, and the black runs through the switch

Brad Kimball what kind of fan/light combo is this? Does the light function separate from the fan etc.? can you get to the wiring of the fan/light? Have you checked the lines coming to the switch? You need to check the voltage across the White and the black Wire. You should have household voltage on the set that comes from the power panel. If you have trouble with that, post some good pictures of the wiring with your QUESTION. It will help us to see what you are dealing with. iFixitでの質問に画像を追加する方法

Brad Kimball that will depend on the way they wired the fan/light. Right now , from what you are describing it is connected together. Remember that you said you have one pair of Black and one pair of White wires, as well as the bare copper ground wires. I would suggest you check for power to the switch first. Measure the voltage across the white and black wire. One of those pairs should have your household current. Just undo the wire nuts and measure without touching the bare wires with your hands etc. BTW the light/fan should not go through a GFCI. Check for power, check your breaker panel first.

Do not connect the white to white via a switch! It needs to stay spliced to the other white.

Since you only have one pair going from the switch, a double rocker switch will not work. You would need to run another set of wires from the fan into the switch box to accomplish that..