<title></title> and <body></body> tags are a requirement for a valid XHTML document of the sort you are playing with.
All I did with your code was insert the <title></title> and <body></body> tags, wrap the tags in the relevant angle brackets and validate it straight away.
Put this lot below your DOCTYPE declaration:
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
Save and re-test on the validator.
<head></head> is a parent element and is considered incomplete without the necessary child elements which, in this case, is the <title></title> tag set. Without the required child element, the parent element is considered incomplete or 'not finished', hence the error message you are seeing when trying to validate your code.