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First reset the SMC and pram

To reset the SMC

Shut down the computer.

Disconnect the MagSafe power adapter from the computer, if it's connected.

Remove the battery.

Press and hold the power button for 5 seconds.

Release the power button.

Reconnect the battery and MagSafe power adapter.

Press the power button to turn on the computer.

Resetting PRAM and NVRAM

Shut down the computer.

Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.

Turn on the computer.

Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.

Hold the keys down until the computer restarts and you hear the startup sound for the second time.

Release the keys.

If that doesn't help try a safe boot

http://support.apple.com/kb/HT1564

Which model macbook? Do you have your original install discs? You can insert the install disc and restart while holding the C key. It will take awhile but you'll get to the screen where you select your language, do that and the next screen will have a menu bar on top. Go to the Utilities menu and select Disk Utility, repair the hard drive. See if you can get that to work.