If you would like to block/unblock a website from being viewed on your Windows computer, follow these steps:
First backup thehosts file.
Open hosts file with notepad.
At the end of the line you can see as per below.
Append the following line at the end
# replace the BlockSitename.com with the site name that you want to block.
Note: That will only stop the domain name to go to the website but if you know the IP address of the site from DnsStuff or NetworkTools then you can browse the site.