From the tech faq
10) Problem: I’ve lost my interface and it’s been replaced by three lines
Not a bug but a feature. Try right clicking on the three lines – you will see that your interface bar pops back up again. If you right click again on the interface bar, you will see it be replaced by the three bars. The three bars represent your health, mana and stamina.
See? Jolie is correct.
Kiya
