the error is saying that the CSSMenuWriter/cssmw_home/menu.php file does not exist at the location that the index.php file is looking for it.
double check that the css menu writer folder has been downloaded to:
C:\xampp\htdocs\computerdesign\CSSMenuWriter
is there a menu.php file at:
C:\xampp\htdocs\computerdesign\CSSMenuWriter\cssmw_home\menu.php