I gave up using the ISO’s a while back because of too many issues - it doesn’t seem to me that they test it well compared to the online installer.
Here’s a few ideas
Check that you have enough disk space… the installer does need quite a bit, in the past I was bitten by this even though the installer didn’t think there wasn’t enough space.
Antivirus software. Try running a full scan on the iso, if that passes then temporarily turn off AV (at your own risk, don’t blame me!).
Have a look at your temp folder - I’ve had some issues with the number of files in my temp folder (not with delphi, other tools). Some apps just don’t clean up properly… try cleaning out the folder.
I’d also suggest not using the currently installed licence file. Every time I did, it bugged out telling me I was not licenced for C++ builder. Installing without using the existing licence file was fine.