You've left it pretty much wide open to crystal balling. One of the more common problems which Intel support claims doesn't happen much is the possibility of a partially removed or partly installed earlier version blocking you. If you are lucky, reinstalling and removing the same version would clear that up. If you send them the logs and they try to tell you which version that was, even the experts may tell you incorrectly. If you can't clear up that way (or by removing all Intel software tools installations), there are more drastic remedies (short of reinstalling Windows), depending on your Windows version.
That's a good point. The temporary files and the installation each take gigabytes. If you have multiple versions and keep temporary files, which are useful if you modify the installation, you use up a lot.