Reinstalling

Hi all,
I’m having to re-install cubase SL3, following a Windows 7 restore to factory settings procedure, owing to a corrupt registry. I must admit to being very much a newbie when it comes to this kind of thing, so I could really do with some advice regarding the re-installation.
I mean, whilst I’ll be using the original disc, is there anything I should do to make sure nothing interferes with the setup?

Will I be required to obtain an updated license before the program can be authorised?

Should I just forget it and go for an upgrade?

Any advice would be much appreciated.

Cheers.

Kj