pstumba,
Welcome to Apple Discussions.
You can try a SMC reset simultaneously hold down the Left shift, Left Contol and Left Option buttons and Power button for a moment. Then restart the computer.
If that still doesn't work, shut down the computer and wait a moment then restart while holding down the Option and D keys which will force the computer to start from the internal drive.
If that still does not work then try inserting the install disc that came with the computer and restart holding down the Option key, then choose the Startup disc when it asks which startup volume to use. You should then see the language choices, choose your language and then from the Utilities Menu choose Disk Utility. In Disk Utility check the S.M.A.R.T. status of the internal drive it should indicate "Verified" if it is OK. If it does not then choose Repair Disk, you may need to run this several times until the drive appears OK. If it still fails then you know your internal drive failed and you have a valid warranty claim. Simply call AppleCare (look in your manual) or make an appointment at the
Apple Store you purchased it from to arrange for a repair.
Regards,
Roger
