I have this gpa program written but I can not get it to work, and I don't know what is wrong. Can someone please help.

<HTML>
<HEAD>
<Title> Rachelle Ahlness </Title>

<Script Language = "Javascript">
var input1 = window.prompt( "Please Enter your average", "0" );

var value1 = parseFloat( input1 );



function qualitypoints()
{
if ( value1 >= 100 )
qualitypoints = 4;
else
if ( 80 <= value1 >= 90 )
quality points = 3;
else
if (70 <= value1 >= 80 )
quality points = 2;
else
if (60 <= value1 >= 70 )
quality points = 1;
else
if (value1 <= 59)
quality points = 0;
}

document.writeln ( "You have " + qualitypoints + " quality points and a " + lettergrade + " letter grade" );

</SCRIPT>
</HEAD>
<BODY>
<p>Click refresh (or reload) to run the script again</p>
</BODY>
</HTML>