I followed all these steps (unistalled CS3, then downloaded the new CS3). After downloading CS3, when I open Photoshop, it takes me to the same Re-activation window from before.
There is no option for me to enter my new serial number and when I click Re-Activate, it goes back to the "Activation-No Connection" message. I don't think I skipped a step, but I don't know where to go from here.
try67 has already provided you with a solution to this issue in his first response: Activation or connection error when starting CS3 or Acrobat 8 beside the installer you have to generate a new serial number for the suite and Acrobat Obtain a new serial number | CS3, CS4 and that will work with the new installer
Please follow all the steps carefully from the link mentioned above and let us know if that helps.