For a little while, I've noticed that my Macbook has been a little low in disk space. I never knew what was taking up so much space, but I always had a decent amount left, so I didn't look into it.

Earlier this evening, I started getting alerts that my disk space was low. I checked my HD, and it said it only had 200+MB left. I was a little confused, because I had recently taken off a disk partition that I was using to run Windows, which freed up 25GB, but I thought maybe I had actually filled it. After a few minutes, it then read Zero KB. I transferred some of my photos to my external HD, and that freed up about 5GB, so then I just left it at that, knowing I wasn't downloading anything or doing anything like that.

A couple hours later, I came back to my computer, and I started getting the exact same warning for running out of disk space. I checked again, and this time it said Zero KB again. The fan was on very high, applications weren't really loading, and I couldn't even load an internet page. I was forced to restart the computer, and when it rebooted I had 2GB.

I sat and watched earlier as my HD slowly but surely decreased, as if there were a hole in my computer and disk space was slowly leaking out. What in the world is going on, and how can I prevent this from happening? Also, my Macbook has a capacity of about 150GB, and currently I have 8GB available. All I really have is music (60-70GB) and word files, plus some applications I installed--some big ones like photoshop--but I really don't know what could be taking up over half of my disk space. Would it have anything to do with this mysterious deterioration?

Thanks a lot for any responses, I appreciate it.