Flashing question mark, cancel, apple, and folder symbol.

Hello,

Try holding the Option key at startup to see if you can boot off the Install Disc to repair the drive, or the c key.

"Try Disk Utility

1. Insert the Mac OS X Install disc, then restart the computer while holding the C key.

2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu at the top of the screen. (In Mac OS X 10.4 or later, you must select your language first.)

Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.

3. Click the First Aid tab.

4. Select your Mac OS X volume.

5. Click Repair. Disk Utility checks and repairs the disk."

http://docs.info.apple.com/article.html?artnum=106214

Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.

(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)

We need to clear some really big files off of it, like Movies, or I suspect some huge logs from something going wrong. 0 KB on the drive can ruin many files on there.

Look at A flashing question mark appears when you start your Mac

http://docs.info.apple.com/article.html?artnum=58042

Since you were getting earlier messages about an almost full hard drive, you should have immediately moved files to the Trash and emptied Trash. Since it showing zero KG, you have corrupted the files and you'll probably have to erase the hard drive and reinstall the system, apps & files. Do you have a backup of the hard drive on an external hard drive?

 Cheers, Tom 😉

This means it can't find your data. This has happend to me before. Turn it off and or unplug it for a day. You will not get this symbol anymore (Hopefully). Hope this helps,Jake.