Why can’t I send HTML mail ?

Why cant I send Email from Hotmail?
Every other function goes fine , but when I try to Compose a message in every HTML mail(Hotmail , Yahoo and so forth) , with the Rich Text Editor ” ON ” ,the cursor just doesn’t blink so I can’t type any words down ! If I switch to ” plain text ” , cursor function as normal.
How could I solve this ? (I have Win XP Pro)