Help please. cpu isn't reconizing free space after deleting files

I don't know what's going on. I was trying to make space on my computer by transferring big files to my external hard drive and I deleted them off my laptop. I only had 250mb of space left so I deleted some files and then it showed I have 16gb of free space. Then all of a sudden when I tried to download files onto my computer it said not enough space please delete files..... and I looked again then it said I have only 250mb of free space left again even after I deleted about 16gb of stuff and the files I deleted have been moved to and emptied out of the trash. How do I reclaim my empty space on this laptop? I'm running OS 10.5.8 if that makes a difference. Thanks for any advice I can get.

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Run Disk Utility > Erase Free Space - if available (it's not in Panther which I'm using, but I think it is in Tiger and later). You can do this same job by booting from your Install disk, and then effect repairs if necessary.

You should also Verify and Repair Disk Permissions - but I'd recommend OnyX Titanium Software for that task.

yeah, I've already done all of the above. It's still not recognizing the free space though that I cleared up from deleting files.

You need either a larger hard drive, or an external HDD formatted to suit either a PPC or Intel machine, you have provided no information on the machine which is a handicap. A hard drive requires a minimum of 15% of hard drive space free to be able to work at anywhere near an efficient level.