Passing A Dynamic Variable To Be Checked?

I have a signup form on a site that does a check on submission of fields to see if they populated and error box if not changes focus to missing field and highlights field name in red.

I wanted to improve on its effectiveness as it only checks 2 fields atm and I wanted it to check some dynamic fields as well

the fields are associative arrays generated via php as follows:-

echo "<select name='nfield[$t]'>
";
for ($i = 0; $i<count($value2); $i++) {
echo "<option value="".trim($value2[$i])."">".trim($value2[$i])."</option>

[Code]....

but this doesn't work, i think it doesn't recognise the nfield[1] syntax

I also wanted to enhance the form somewhat as atm it only displays one error popup at a time, so if the user has missed out a few fields they will get an initial popup, try and submit again and then get the second popup for the other missing field.

Can my code be modified to show a list of the missing fields and highlight all the titles in red (and if possible change the background colour of the input boxes or border the input fields in red etc)?