Missing some Javascript in WIN98 OS

I am experiencing difficulties with some of my programs (prime ex: I cannot automatically delete email in my Yahoo email account-the “check all” and delete functions don’t work. Yahoo tells me these are Java-based and I need to be certain my Java-Script in enabled. It is, as far as I can tell. A friend says he believes part of my Javascript is missing. How do I find out if this is the problem and how do I fix it?