Cannot create files/folders.

My Macbook has been much slower than usual lately, and today it just stopped creating files. When I try and open Skype, it tells me it cannot create the users file, when i try to open itunes, it tells me it cannot create the itunes folder.

I have repaired the disk permissions and verified the disk. Verification came back okay. I'm now at a loss as for what to do. I can't download any new files (it tells me that I'm out of disk space, while I have 50 gb's free), so downloading anything to fix the problem won't work.

Thanks in advance guys..

 

Working on the backup now, thanks. I'll have to try repairing the permissions tomorrow. Replacing the hard drive on this thing is going to suck..

 

Okay. Something was very messed up. After trying everything and just not believing it was the hard drive, I just went in and set my permissions to allow all. Now everything's working just fine. But it's not finding my USB hard drive, and it's not showing my system disk on the desktop. I'm just wanting to go back and restore now that I figured out what the problem is.. *sorta*

*edit* Okay, so everything's not just fine..

 

I actually got it working. Just did a completely fresh install off of my Snow Leopard disk, and it's working better than it has in months. It's the strangest thing. It's almost like a virus or something. I'd fix the permissions, and they'd get messed up again. Thanks to everyone for the help!