how to block sites in windows

open run
and enter
%windir%\system32\drivers\etc

then inside these folder there is
hosts file
copy these to desktop
these file look like these


# Copyright (c) 1993-2009 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
#      102.54.94.97     rhino.acme.com          # source server
#       38.25.63.10     x.acme.com              # x client host

# localhost name resolution is handled within DNS itself.
# 127.0.0.1       localhost
# ::1             localhost

and in the bottom most position if you want to block facebook add these 

127.0.0.2 facebook.com

127.0.0.3 www.facebook.com

#you can also add other website like youtube by

127.0.0.3 youtube.com

127.0.0.4 www.youtube.com

{FILE PROBLEM NOT AUTHORIZED}

copy hosts file to desktop and edit the file the file should look like these

# Copyright (c) 1993-2009 Microsoft Corp.

#

# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.

#

# This file contains the mappings of IP addresses to host names. Each

# entry should be kept on an individual line. The IP address should

# be placed in the first column followed by the corresponding host name.

# The IP address and the host name should be separated by at least one

# space.

#

# Additionally, comments (such as these) may be inserted on individual

# lines or following the machine name denoted by a '#' symbol.

#

# For example:

#

#      102.54.94.97     rhino.acme.com          # source server

#       38.25.63.10     x.acme.com              # x client host

# localhost name resolution is handled within DNS itself.

# 127.0.0.1       localhost

# ::1             localhost

127.0.0.2 facebook.com

127.0.0.3 www.facebook.com

and replace it with original hosts file

now enjoy