I would be willing to bet be willing to bet that you did not check for power and ground at the window switches before replacing them.
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Please read this article before continuing: What Else Could Be Wrong?
I am assuming that you have the 4 door model since you specified "both" and "front". So this advice will be based on that. If you have the 2 door version, this could be very different.
If the rear windows are working and the front windows are not, that eliminates both the power source from the circuit breaker to the master switch and the ground circuit to the master switch, The only "component" that could cause both of these circuits to malfunction at the same time would be the master switch. You could, however, have separate failures of each of the window motor circuits between the master switch and the window motors. GM has had more than their fair share of window motor/regulator failures. This type of failure is not likely to occur on both sides at the same time. This would more likely work something like: Passenger side quits, then several weeks or months later, the driver's side quits. You could also have broken wires inside the umbilical between the body and the doors. With the older cars with the master switch in the driver's door, one broken wire could take out both doors. This does not apply to your vehicle, however. Again, this would also not be one of those things that would cause both sides to go out at the same time.
So to wrap it up, you need to check for power and ground moving into and out of the master switch at the correct locations and under the correct switch operating positions. This will require you to get your hands on the wiring diagrams for your power windows so you know what is what.
If the power and ground is ok at the master switch, then you need to remove your door panels and check for power and ground at the window motor connector. If you are missing either power or ground at any point, then you will need to do a wiring repair. If power and ground is available at the window motor connectors, then you need to replace your window motors and/or regulator assemblies.
2-door diagnosis is similar, but you cannot eliminate "source" power and ground to the master switch by operating the back windows. You will have to test for it at the master switch.