E-mail problem!! Help, please!!!?

Every time I try to write an e-mail on Yahoo Mail, whether using compose or reply, it skips letters. I type normally and a lot of the keystrokes don't register. It isn't the keyboard, as I use the same one for everything and it is fine everywhere else, on or off yahoo.

My wife uses the same computer with her yahoo! account and doesn't have this problem. Her account name is the same as mine with a "1" added, and we're using the same password for each account (how trusting!!!) Could any of this be causing this problem? It's not the computer, has to be an error in my e-mail account somehow. My account was created first. It's been happening since we got onto yahoo. I tried asking this once before and was asked for "more details". What other details are needed if this isn't enough?

I can't send e-mails like this, I have to type each letter/space one at a time and check if it registered.