Download the offline installer (and be sure to check "Offline Installer" prior to download)
Re-try the installation
If the above suggestions fail, here are some further troubleshooting measures to try:
Verify that your device meets the minimum requirements to run Dropbox
If you're on Windows XP, verify that you're not right-clicking the installer and selecting "Run as..."
Check that you're not encountering network issues, which can be caused by any of the following:
A firewall blocking full download of the installer (solved by manually entering "DropboxUpdater" as an exception in your firewall)
Do I need to configure my firewall to work with Dropbox?
A block due to proxy or antivirus software
Why can't I establish a secure connection?
Dropbox for Business team members may encounter issues caused by local admin policies (contact your team admin to check)
If you've tried all of the above troubleshooting measures but you're still encountering an install failure, or if you're seeing an error message like the one below but with a specific code number, please check the Dropbox forums or contact Dropbox support.