Thank you for your quick responses!
Dh managed to fix it. He thinks it was a problem with a template. I have no idea what that means.
Oh, and I had already tried the turn-it-off-and-turn-it-back-on approach. That's always the first thing I do! LOL!
It wasn't the insert key. It was actually typing letter upon letter. So, I ended up with big black blobs. In other words, it wasn't replacing letters over each other. It was keeping them all!