Disk is full but, I have nothing on my laptop?!

I keep getting startup disk full messages and I cleaned about 4GB off my laptop, but for some reason i have 118GB of other?!?!?! What is other? I have 5 movies, 1 backup, 100 itunes songs, and around 60 photos, and only 4 applications (each application takes about 2GB) Thats only around 30GB right there. (I removed all of my mail, I had 4300 emails, gave me about 400MB from removing them) Yet everything else on my laptop, has to be on it, it came with it. So I still don't get why I have so much GB taken up in the "Other" section yet I have nothing on my laptop. Is there something I'm not doing correct? (And yes I emptied the trash for everything I deleted) Or is there just something wrong with my laptop?