No more space? Help

[doordoor123]

I edit movies a lot and while importing a movie onto FinalCut, my computer had a message saying there was no more space on the hard drive (startup disk?) and I needed to delete some stuff. I put almost everything onto an external hard drive, but I still get the same message. The available space has been fluctuating, but it has now finally settled at zero bytes. My laptop has 319.21 GB, but I can't seem to figure out why I have no space available. I either deleted stuff through the trash or put it on my external hard drive. There are few things that I have kept on my laptop, but it still says I have no room available.
I don't know as much as I should about Macs or computers (other than with editing) so I can't really say anything else. Any help would be much appreciated. Thank you!

[DeltaMac]

Be sure that if you moved a lot of files to an external hard drive, then put THOSE files in the trash from your internal drive. They STILL take up space, even in the trash, so be sure to empty the trash, as you don't really accomplish anything until you actually empty the trash. If the hard drive is completely filled, even emptying the trash may not be do-able.
Absolutely restart into Safe Boot mode, by restarting while holding the shift key. You will boot to a login window, even if your Mac normally bypasses that login window. Log in. Safe Boot mode MIGHT give you enough "wiggle" room to empty the trash, and your first task is to empty the trash - then immediately restart. If this allows you to go back to normal work - do NOT continue until you verify that there's enough space for the system, plus your normal video file use. Looking to the future, a good rule of thumb is a minimum of 15% of total space left free. If your Hard Drive is 320 GB, then try for at least 48 GB free.

[doordoor123]

My trash is empty. I've deleted everything, but it now says I have 14.2 MB. I don't know why I don't have much room. Is there anything else I can do?

[DeltaMac]

It's possible that the space is being reported inaccurately.
Boot to your OS X installer DVD, and run Disk Utility from the Utilities menu. Choose your hard drive, and run Repair Disk (different from Repair Disk Permissions)
Here's a couple of places that you can remove some files, probably get some more space back. Your own user folder, then the Library folder. Drag the Caches folder to the trash, and again, empty the trash. Same thing at the root of your hard drive, then the Library folder in that main directory. Drag that Caches folder to the trash. Your system will usually ask for your password, so provide that. Empty the trash again. Those are active caches, so some may not let you empty the trash until you restart your Mac.
The combination of those two Caches folders may give you some room, so you can continue to move more of your video files OFF of your internal hard drive, to your back up. Don't forget, especially for large files, that those files remain where they are, and you are just creating copies on the other backup drive. Don't forget to trash those files on your internal drive once that copy completes - and finally, empty the trash. It takes some time. There are other techniques, and also utilities such as OmniDiskSweeper, which can help you find the locations of large files to help you clean up that drive.