From what you describe it seems that ArchiCAD can not access the Windows registry for some reason. The "registering ArchiCAD..." phase is when ArchiCAD tries to create the necessary Registry keys. This takes place as the last step of installation, or - if the keys are missing - when you start ArchiCAD.
Check if you have administrative rights on the computer, and if you do and the same happens, maybe you should do a system repair to fix your registry.
Greg
Gergely Kmethy
VP, Customer Success, Graphisoft