I've just installed the application on a 64-bit Windows 10 PC and it went through without any kind of errors. I even tried changing the installation folder to a different partition and still no issues.
Make sure that you have administrator privileges on your Windows and that you select Run as Administrator when you install WatchPower. Additionally, I've noticed that the application uses the Java Runtime Environment, so you could try installing it separately.
Lastly, the installation log should be found in the folder where you installed the application.