Log in as root to a Vesta installed server via terminal.
Open the configuration file using any text editor:vi /usr/local/vesta/conf/vesta.conf
Add the following line at the end of that configuration file:
FILEMANAGER_KEY=’ILOVEREO’
Save and exit the file.
Try to log out and re-login to Vesta panel and you will be able to see the file manager option now.