Hi mvang,
Usually this is a permission problem that Admin Tools will fix, but I can see if you can't upload that, you can't fix it that way!
Can you use your file manager or FTP to access the server and check to see that your folders are CHMOD 755 and your articles are 644.
Make your configuration.php file 644 while you're working with it. You can change it to 444 when you're done if you want added security.
Also go to your Global Configuration and see if the path to your tmp directory is there and that it is correct. Make sure the tmp directory is 755 as well. If you don't have a tmp directory, create one and put the path to it in the global admin.
Try that and see if it makes anything work.
Cheers,
Ed