Sounds like you may have a malware issue. Take a look into running a malware scan and also check your htaccess file which is accessible through the file manager or via ftp. This file can be renamed to diagnose the issue which disables it temporarily.
There's not one direct answer for dealing with malware on websites. Removing malware on sites is really dependent on the comfort level you have in dealing with your site and it's files. GoDaddy does offer paid solutions to help with this, like Website Security, however, it's not required that you use it.
The following help article might give some more insight and steps you can take: https://www.godaddy.com/help/my-website-was-hacked-what-should-i-do-19945
Hope that helps.