Since the release of SU 2017, there has been a tidal wave of posts from people who encountered problems with SU because they did not install it properly on Windows. The only correct way is to right-click the installer and select “Run as Administrator”. It is not enough to be logged on as an adminstrator.
This requirement (which is not unique to SketchUp) is because modern OS’s have upped their security requirements to protect against malicious code that tries to modify crucial system areas such as the registry. To reduce the likelihood that malware is trying to attack your system without your knowledge, Windows requires an elevation of privileges beyond those routinely granted to an administrator (Mac OS X does the same thing). The right-click menu selection tells Windows that there is a live person involved who at least claims to know what they are doing.