The serial number should already be stored in the operating system. Consequently, you should be prompted for the serial number when doing the reinstall. What are the problems you're having that made you think reinstalling was necessary?
My computer is on the verge of crashing for lack of space, consequently i would like to wipe my drive and begin again. I would like to move all my catalogues to an external drive and save them this way enabling me to do a reinstall and then later be able to access these folders for later use. i think the problem is that i have numerous catalogues and have no idea how this happened. My drive should not even be full, it appears that the overflow of catalogues with all my work have filled the drive to its capacity and i dont want to lose those files but when i tried to consolidate them and only use the latest catalogue because LR stores several files for each catalogue i messed up the programs ability to do edits. So i would simply like to kill my computer and restart with my fresh copy and go from there as i have limited time to be up and running again. it is very frustrating and catalogues SUCK they seem to take quite a bit of space on the drive and should not as i only need the exported files saved so that i can re access them later if needed. I can always do a new import of photos in that batch if i need them in the future and am just really trying to get it done in as speedy a way as possible. It is very frustrating that although i thought i saved the original e-mail with my serial number that i can not find it anywhere, and although i registered the product when i purchased it Adobe does not show that it is registered and so no listing of my original serial number exists there either. I am beginning to feel like this is set up to make a person re-purchase the product and i cannot afford to do that. I also do not want to advance to the online version where you pay a monthly fee for the product i really like 5.7 and have no desire to upgrade as the program 5.7 has always been adequate for what i do with my photos. Can you think of anything that i can do to expediate this process. I seem to be getting mo help from Adobe at all, and will be calling them tomorrow as their customer service is only available monday through friday. ???
Are you using a Mac or a Windows PC.
Simplest thing to do is DELETE un-needed files from the drive to free up space. As to multiple catalogs only the User can do that. Lightroom doesn't arbitrarily create catalogs. The Catalog is actually fairly small. My Catalog of all my images from back as far as 2006 is only 237MBs.
Right now Lightroom 5.7.1 is the most current release and it is a the same whether it is the Stand alone or the subscription version.
As I posted in another thread "There are millions of People using Lightroom 5 without any problems what so ever, me being one of them". So the problems you are having boils down to your computer, user error and or lack of knowledge on how to properly use Lightroom and how Lightroom work.