My usb ports for Mac OS X version 10.6.8 are not working

You've probably already rebooted the system.

Reset your SMC and PRAM.

Reset PRAM:

1. Shut down your Mac.
2. Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

If that doesn't do it, see this Apple note on ports.