Problem with arial font

Hi,

Whenever, I use the arial font the characters displayed don't match up to what I'm inputting. For example, pressing the 'q' key will enter a 't', pressing the 'w' key inputs a 'z', etc. Also, sometimes these incorrect characters will begin to overlap. However, when I change the font to bold, this problem corrects itself. Anyone come across is? What's the fix?

Thanks.