If you notice that you are always getting redirected to the website files.null.com, it is possible that an adware is causing these redirects. Files-null.com will show malicious ads tricking users to download potentially unwanted programs. This adware will attempt to commandeer your browser search and homepage. It will then send you to malicious websites to get money from you or infect your computer further. It may also prevent you from changing your settings back.
The adware Files-null.com is usually installed through bundled software without you knowing. Remove it immediately!