First Person Controller doesn't work properly.

Hi Guru. I'm a newbie of unity dev. The problem I got is after putting First Person Controller in my project and I hit the play button. I just dragged and dropped to place the FPC.

Keyboard control(WASD) is ok, but moving mouse doesn't change any directions so I clicked the left button. suddenly it just looked down. To change the direction I should click the left button. That's it. I couldn't change it back to see ahead.

I tried to create the project again, but haven't solved yet. pls give me some advises..:( Thank you all in advance.