1. Re-register your Windows Installer Service by clicking the 'Start' button and choosing 'Run.' Write 'Msiexec/unregister' into the resulting window and hit the 'Run' button. Close all windows. Click the 'Start' button again, followed by 'Run.' Insert 'Msiexec/runserver' and hit the 'Run' button. Close all windows and restart your computer. If you still receive Error 1720, proceed to the next step.
2. Visit the Microsoft website and download the newest Windows Installer by searching for it and clicking on the download. Once it is downloaded, double-click on the set-up file to install it on your computer. Restart your computer.

3. Ensure that Windows Installer Service is running correctly by clicking on the 'Start' button and choosing 'Run.' Type 'services.msc' into the box and click the 'Run' button. Browse around for the Windows Installer Service. If it is not running, right-click on its icon and click 'Properties.' Locate the 'Startup Type' option and choose 'Automatic.' Close all windows. If you still receive the error after this, consult a computer professional.