If your operating system is Android version 4.4, and have tried unsuccessfully to install WhatsApp, it may have been generated a folder that keeps you reinstall the application.
This folder is called com.whatsapp, and is located in / data / data (as explained on the website WhatsApp). The only two ways to remove it so:
· Having a rooted phone (in this case you can find the folder and delete)
· Reset the phone (Settings> Backup and Restore> Factory data reset)
Attention! Remember to reset the phone to factory data means losing all data (phone numbers, messages, call log, saved files, etc) it contains. Before you proceed make a full backup of phone content.