1tb hard drive but listed capacity is only 12gb?

Where are you seeing only 12GB? Disk Utility o somewhere else?

~Lyssa

Too little information, so I'll give you a general solution that should work assuming the drive is not malfunctioning.

Clean Install of Snow Leopard

Be sure to make a backup first because the following procedure will erase

the drive and everything on it.

1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came

with your computer. Insert the disc into the optical drive and restart the computer.

After the chime press and hold down the "C" key. Release the key when you see

a small spinning gear appear below the dark gray Apple logo.

2. After the installer loads select your language and click on the Continue

button. When the menu bar appears select Disk Utility from the Utilities menu.

After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive

size.) Click on the Partition tab in the DU main window. Set the number of

partitions to one (1) from the Partitions drop down menu, click on Options button

and select GUID, click on OK, then set the format type to MacOS Extended

(Journaled, if supported), then click on the Apply button.

3. When the formatting has completed quit DU and return to the installer. Proceed

with the OS X installation and follow the directions included with the installer.

4. When the installation has completed your computer will Restart into the Setup

Assistant. After you finish Setup Assistant will complete the installation after which

you will be running a fresh install of OS X. You can now begin the update process

by opening Software Update and installing all recommended updates to bring your

installation current.

Download and install Mac OS X 10.6.8 Update Combo v1.1.

The disk may have a 12GB partition as HFS+, and rest may be free space. Run diskutil list in Terminal or Disk Utility as suggested.

I'm assuming the computer is running right now. If you go to Applications>Utilities and open Disk Utility, what do you see listed for disks on the left-hand side?

~Lyssa

Okay - your computer sees that you have a 1TB drive.

If you go to the Apple menu, choose "About This Mac" and then "More info...", do you get a small window that says "About this Mac" with a picture of the computer on it?

If so, click on the Storage tab. Does the computer see 1TB there also?

~Lyssa

If you have less than 294 MB available, your hard drive is running (has run) out of space; you need to have an absolute minimum of 10 - 15 GB of empty space at all times for the OS to perform properly.

You must have a lot of music or videos or pictures? You will need to delete or move those to an external hard drive. Everything you copy, download, install, or "park" on your hard drive takes up space, and slowly there won't be any space left.

Please post a screenshot from Disk Utility showing this info:

Okay - your Mac did something a little different than mine; I'm on 10.7 here and couldn't remember if that box would come up.

Your Mac is seeing your drive as 1TB, and is it really showing that only 293.5 MB are available? If so, it's no wonder it's having issues as the drive is almost entirely used up!

Follow babowa's instructions to post a screenshot; we need to figure out where your space has gone.

~Lyssa

There is something really strange going on. Your hard drive is showing as one partition only, yet it shows only 291 MB available, but only 11 GB used out of 999. That is very strange. Okay, try another screenshot: highlight your 1 TB (top listing on left), select the Partition tab and post the screenshot:

I have a few ideas for what you could do for troubleshooting from this point, but is it feasible for you to go back to the store and have them look at it again? Something did not go right when they reinstalled the OS for you. Those numbers do not add up at all, and they really should be the ones fixing this.

If getting to the store isn't an option, do you have the install disc(s) for your Mac? Wiping the drive & restoring from a Time Machine backup would do the trick. It's an extreme measure but should do the job.

~Lyssa