First, a bit of background: VideoReDo essentially became abandonware after the passing of its original creator, DanR. While the official company servers are long gone, a former employee generously set up a manual activation site to help existing license holders keep their software running. Is There a Truly "Free" Activation?
Activation is effectively free in the sense that you don't have to pay again, but you must have your original 60+ character license key and name.
If you have your original key, follow these steps to reactivate:
Instead of clicking the automatic button (which will fail), look for the Manual Activation button on the left.
Go to the manual activation site in your browser and enter those two values.