Delete all the fonts except the system ones. Delete (all!) Adobefnt.lst Adobefnt ??. Lst files. Then reinstall the fonts as needed. Just in case, assign the TEMP environment variable in the control panel to the "shortest path", such as c: \ temp.

Was CS3 installed on the same machine? Or CS5 is installed on a "clean" Windows..Could you write more detail about the "old version"? Perhaps, there are any conflicts. Download a cleaner from the official site. If AI doesn’t install on the clean Win, then you should connect with adobe support, I suppose. But first test your RAM.
The last way – run a third-party. I think a good one might help. Recovery Toolbox for Illustrator - this one saved my data once https://illustrator.recoverytoolbox.com/ but I had a completely different problem. I cannot promise that it will help you in your case, read closely about it.