Consider deleting the extra set of <!DOCTYPE>, <HTML> and <HEAD> tags. I'm not sure if they're the source of your js errors (you didn't tell us what the errors were) but they certainly aren't helping.
You are missing spaces on case"F" and case"D". They should be case "F" andcase "D"`. This isn't an error per se, but best to keep it consistent.
Your <body> tag is also left unclosed. This is probably the source of your errors.
Edit:
Some more stuff:
<form name ="gradeForm""action" =""> should be <form name="gradeForm" action="">