Hard Drive Usage Problem!

Hello,

I have a macbook pro mid 2009, i recently upgraded to Yosemite. After a few system changes and some clearance my Mac became a little bit faster. Now i am doing disk erase using CCleaner.

Now my problem is the following. When i go to -> About this mac -> Storage, i see that "Movies" are about 40GB! The thing is that i have no movie files saved on my mac! What is going on? I tried everything about system clearance. But 40 GB on movies?

Please if someone know something about it, feel free to help me a little bit. I try so hard to maintain my macbook pro clean and fast because i am a uni student and i cannot afford a new mac for now. Even the volume and light icon don't respond immediately!

p.s. Sorry for my bad English, i hope you can understand as many as i wrote above.

George