Problem

When trying to install Dropbox on a Windows computer, it asks for an admin username and password.

Solution

If you can use right-click elevation, then right-click the installer file and choose Run Elevated or Install Elevated. If you don't have right-click elevation rights, then you can just hit cancel on the window asking for the admin username and password. Dropbox will then ask you if you want to continue without administrator privileges.  Click Yes to install.